Where do i set the environmental variable?
Different places for different operating systems; you didn't mention what OS.. In Windows, I recall it being in a tab under Device Manager. Ask Google.
I use Linux.
The map update is very slow and pixelated. Should I reset something?
That is why you need to set that env var.
Where can I find the current version?
?
Where is the file data.qmdb located?
For some OS's capitalization is important. Just use your OS's GUI search utility to find Data.qmdb
Or from a command prompt in Windows you can:
dir c:\Data.qmdb /s/b
From a Linux command prompt (terminal) you can:
sudo find / -iname 'Data.qmdb'