can i update my mac os x yosemite 10.10 5??? It tells me I have no updates available but it will not let me download certain apps because I need to update...

The App Store Updates page only informs you of updates available for the OS you are running.

Installing a newer OS is called an upgrade.

Which OS you can upgrade to will be governed by which model and year your mac is.

Click on the  top left of your screen click on About This Mac to find out the year of your mac.

For older OS’s,

Open Safari and click on this link, 

How to get old versions of macOS – Apple Support

Go to Check Compatibility to see if your mac qualifies for the OS upgrade you want.

Then go to the Download OS section and click on the OS you want to install.

If you want to or are able to install Big Sur, open Safari and click on the link below.

How to upgrade to macOS Big Sur - Apple Support

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you are considering upgrading to Catalina or Big Sur be warned they do not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see

if they are providing 64bit updates or alternatives.

This is something you might want to keep in mind. There are updates and there are upgrades. They are different. An update is a file to update an existing OS. An upgrade is a file that installs a newer OS than the one you currently have. Each may require a different method of accessing them. Upgrades often require that the link are accessed from the Apple App Store or from Apple's web site. Note: be sure to use only Safari when doing any of these downloads. Also, I do not recommend using Wi-Fi as it often causes the file to become corrupted because the files are so large and Wi-Fi is much slower than a wired Ethernet connection. In summary, you appear to be needing to do a system upgrade to a newer operating system, not an update.