Macbook pro mid 2010 Maverick 10.9.5

For software upgrades...

MacBook Pro mid 2010 can run from OS X 10.6 to macOS 10.13, and 10.13 would usually be the preferred release.

It’s only the latter few releases or macOS that are currently getting security patches.

Click Here For 10.13 High Sierra Upgrade Info—you can upgrade any Mac running OS X 10.8 and later directly to 10.13, for those Macs that support High Sierra.

If you really want or need an old OS X version—and I don’t recommend this approach for this case—then Click Here for How to upgrade to OS X El Capitan.

Older releases are not available from Apple, if they’re not already (still) in your previous purchases in the Mac App Store. And I’d definitely not recommend upgrading to anything older than El Capitan. Not for this case.

For hardware upgrades...

An SSD upgrade will be a bigger performance upgrade than a memory upgrade, in many cases.

Fast hard disks can do ~150 I/O operations per second (IOPS).

You don’t have a fast hard disk here, either.

Fast hard disks hot, power-hungry, and are 15,000 RPM with a fast bus and a big cache.

Recent SSD storage devices routinely runs at 100,000 I/O operations per second.

Or more.

SSDs faster than 350,000 IOPS aren’t unusual.

As compared with ~100 IOPS for a laptop hard disk drive, when you’re reading and writing files and data.

Not that the added memory won’t also help. It will. But not usually as much as an SSD.

I'm not entirely certain what version you're seeking to upgrade to here, nor what issues you're encountering with the Mac App Store, but I probably would not wipe and reinstall here based on what seems to be the situation and the intent here.

MacBook Pro Mid 2010 and later are supported on High Sierra. That's the version you'll want to upgrade to, in most cases. A direct upgrade from OS X 10.8 Mountain Lion and later is supported. Check your key app compatibility, check that you're running Microsoft Office 2016, 2019, or 365—if you're running Office, and check that your printer and scanner device vendors have drivers available for your devices.

Downloading certain older OS X and macOS versions is still possible, though Apple makes finding that somewhat more difficult within the Mac App Store as later software is preferred and is supported with that Mac.

If you still have a hard disk drive in that MacBook Pro, an SSD upgrade will usually provide a significant performance boost.

Whether an upgrade is worth it is your call. As was mentioned earlier, a high-end hard disk drive (HDD) can sustain ~150 I/O operations per second. You don't have a high-end 15,000 RPM large-cache HDD here, either. Those HDDs are power-hungry and hot. Recent SSD storage routinely operates at 100,000 to 300,000 I/O operations per second, and variously faster. That performance difference can make up for a lot of slowness elsewhere in a system configuration, when replacing an old HDD. If you're already operating with an internal SSD and not an HDD, the performance difference will be (much) smaller. Again, whether this upgrade is worth it depends on your preferences, your budget, and on how long you plan to keep this Mac.

As for whether your Mac can be upgraded further, a MacBook Pro mid 2010 tops out at macOS 10.13 High Sierra. An upgrade to macOS 10.14 Mojave is not supported on a Mac this far back. Nor is the Catalina preview (macOS 10.15 beta) supported on this hardware.

I agree that High Sierra would be the best OS to upgrade to. Once you do that, see if the computer is still slow before doing anything else. Hardware may speed up the computer, but the problem could also be software related. If it is still slow after the upgrade, try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account 

Safe Mode - About

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply.        Pastebin

Etrecheck – System Information

If you go to the menu/About This Mac, what OS version shows there?

Have you checked the Applications folder to see if the High Sierra installer is there?

Have you tried downloading in another admin user account or the Safe Mode?

Safe Mode - About

Already-installed could well mean already-downloaded, but not installed. Look in Applications for an Install macOS High Sierra app.

The corruption here is likely central, though.

Which may be software, or may be failing hardware such as a failing hard disk.

Failing hard disks can show as performance degradation, app and system crashes, beachballs, and related misbehavior.

I would not bet that an upgrade will resolve a corruption, and it won’t resolve failing hardware.

You could and probably should try running the hardware diagnostics here: Mac Introduced After June 2013; and Mac Introduced Before June 2013. Diagnostics will will show overt hardware failures, but can miss other sorts of hardware failures.