Had to reinstall Unity, forgot version number

Greetings,
Lovely Windows crashed so I had to repair it by losing the programs and keeping the files.
Along the way I forgot what version of Unity I was using. It was a recent 5, but not the most recent.
I understand that I can run my game on the newest Unity, but the version I had did work pretty well I do not wish to change the version, I want the same. How to find out which version i was using?
If I have no other means, can I downgrade later to an older Unity 5 and expect it to work?
Regards
EDIT: What about upgrading the projects? does it mess up something, or will everything be fine?
I spent 3 months, 14-16 hours a day making those games, wouldn't like to lose them

 

It's not ideal, but if you download the most up to date version, in the startup window it shows which version number each of your projects was last saved in.

 

You can get the version without downloading Unity by checking ProjectVersion.txt under the ProjectSettings folder.

 

If you want to update, is better a final version U5.3.6 than a U5.4.0final1 or U5.5.0beta3 .
To know the Unity vr in windows you can go to C:\Program Files\Unity and right click over Unity.exe icon , then select Properties. Look for the tab Info or Details and there will be the version number. Also is possible to go to the Windows Control Panel select: Programs and Features, and there is a chance Unity is there and it version.

 

Thank you for your help. By checking the project version folder I got it, it was 5.3.5f1. I shall download that in the first place. If I need to update it, I can do it, but if I continue on the most recent build, there is no going back

 

Amazing.