490GB of 'Other' Storage

Get Correct Storage Information

Do not use the information from the Storage section of the About This Mac dialog. Ignore the Storage information as it is typically wrong. To find out the correct information for any disk: Select a Desktop disk icon. Press Command-I to open the Get Info window and look at the topmost panel displayed. You will find the disk information displayed for Capacity, Available, and Used. If you have more than one disk/partition then repeat for each one on your Desktop.

The categories found in the Storage section of About This Mac is simply an arbitrary way of displaying files on your drive. There are no such categories actually on the drive.

How to Free Up Space on The Hard Drive

1. You can remove data from your Home folder except for the /Home/Library/ folder.
2. Visit The XLab FAQs and read the FAQ on freeing up space on your hard drive.
3. Also, see Freeing space on your Mac OS X startup disk.
4. What is 'Other' and 'Purgeable' in About This Mac?
5. Files That Make Up the 'Other' Storage Category, and How to Remove Them
6. Free up storage space on your Mac.
7. See Where did my Disk Space go?.
8. Be sure to Empty the Trash to recover the space.
9. Replace the drive with a larger one. Check out OWC for drives, tutorials, and toolkits.
10. Use OmniDiskSweeper or GrandPerspective to search your drive for large files and where they are located.

See if this is it...

Purging local backups

Please note that although this doesn't affect your remote backup from Time Machine, this will get rid of the redundancy (at least until the next Time Machine backup) that a local backup disk will provide. If you need such redundancy or are worried about the recovery of your data then you would be best served to let macOS determine when to purge these files.

Start Terminal from spotlight.

At the terminal type tmutil listlocalsnapshotdates.

Hit enter.

Here, you'll now see a list of all of the locally stored Time Machine backup snapshots stored on your disk.

Next you can remove the snapshots based on their date. I prefer to delete them one at at time. Once my "System" disk usage is at an acceptable level, I stop deleting but you can delete all of them if you want to reclaim all of the disk space.

Back at the terminal, type tmutil deletelocalsnapshots YYYY-MM-DD-HHMMSS , where will be one of the dates from your backup. This will be in the form of xxx-yy-zz-abcdef. Try to start with the oldest snapshot.

Hit enter.

Repeat for as many snapshot dates as required

http://www.thagomizer.com/blog/2018/03/27/cleaning-up-time-machine-local-snapshots.html

You have a lot of space taken up in your Users folder which contains the separate Home folders of each user on the computer. I would assume you have lots of space on the disk taken up by some things stored on the computer but It's impossible to know what because it is shown to be in Other Users. I can't tell much without physical access to the computer. If you can't find where you have all the space in use, then you should take to a professional to look at it.