To use this mod, Open up your Silent Hill 2 Folder by right clicking the game on steam > Browse Local Files. 
From here, Drag and Drop the "SHProto" folder into your game directory.
Optionally, you may also do it manually by again going into your "Silent Hill 2" Game directory > "SHProto" > "Content" > "Paks" > "~Mods". 
From here, drop the 3 files "HEALTH DRINK FULL HP_P" into this folder. 
If you DO NOT have a mods folder, create one by creating a new folder, and naming it "~mods". 

TO UNINSTALL
To remove this mod, delete the 3 files "HEALTH DRINK FULL HP_P" in your "~mods" folder, same location as above.