They weren't installed seperately, they were both installed in MTA San Andreas folder. I could seperate them, though, if I'd know which files belonged to the old MTA and which ones to the new MTA...
When I opened up every folder and looked for client.dll, which was in the old mta section, I renamed it to oldclient.dll. When I tried to start the map editor in new mta, it still couldn't start a local server (failed to load library blahblah..) plus I couldn't play no more.
I will take some screens to show you how it's installed right now.
Program files / MTA San Andreas:

Program files / MTA San Andreas / MTA (dunno which one, probably new one, cause in the file 'console' it says "votemap race-wipeout"):

Program files / MTA San Andreas / Mods (place where the old mta maps used to be saved (in all those map_editors)):

Program files / MTA San Andreas / Server (not sure, but I think from old mta):

Program files / MTA San Andreas / Server / Mods:
