Upgraded to v8.3.6 but getting login invalid

Hi I upgraded from 8.1.5 to v8.4.3 (getting a php problem-when I stare and compare, folders are missing....only seeing api, db, docs, external, index.php license.txt leadme.txt--->I'll digress for now) I'll deal with that after reviewing the forum.

so in the meantime I upgraded to 8.3.6 but getting login failed

I've tried the following :
Removed location in tool per manual

Seeing Migration in process (only admin)
All proceeds well except when i get to the login screen, I put admin /admin then ok

Getting "invalid login"

I tried this a few times and also restart my computer jic, still get the above message

Thanks for your assistance in this matter

I admit, I'm not tech savy

I kept all versions in a separate folder named (old) because I still don't know how to backup as of yet (going thru the manual until "It Clicks)

What Ive been doing is the following:

I move old versiotn out tof EasyPHP folder and then Unzip new version under the EasyPHP

should I go back to that folder (I believe its 8.1.6)that I had a successftul login, then override that copy with new version?

Thanks for the quick response

Ok, I was able to find the good version (it wasn't V8.1.6 version as I previously thought) but I'm successfully able to login in and will upgrade. Thank You