From the start menu, open Run (or press ⊞ Win+R).
Type regedit
Find HKEY_LOCAL_MACHINE folder
Go to the SYSTEM folder
Go to the ControlSet002 folder
Go to Control folder
Go to Session Manager
Go to Environment folder
Then, inside Environment folder, double click Path
The previous Path should be there.

source: https://superuser.com/questions/523688/deleted-path-environment-variable-how-to-restore
