Why do I see two versions of photoshop?

[quantum 123]

Should I uninstal one?

[gener7]

I'd say "No". It won't hurt anything and if 22 hits a bug, then you can fall back on 21. Especially when it comes to 3rd party plugins that have not been updated for 22, or if you didn't import previous settings.

It used to be deleting previous versions was the default, but now Adobe keeps it and allows the user to decide later.

[quantum 123]

Yes but it will fill up my system won't it?

[Peru Bob]

It doesn't take up that much room.  If you are so short of space that it does, then you will need a larger hard drive very soon.