@MeZZoO
Unzip the new file and copy all the files to their respective ‘l4d’ folders, or just auto-extract them if you know how to do that procedure.
The path for the l4d folder is as follows:
\left 4 dead\left4dead\addons\sourcemod\scripting
Copy your script file called “l4d_useful_upgrades.sp” to that folder.
Next, drag and drop the script onto the “spcomp.exe” file (that file is the compiler for your version of SM). This will compile your file to become “l4d_useful_upgrades.smx”. After that, just move the smx file to your plugins folder. And that’s it. You’re ready to go. EDIT: There is also help here, if you care to read it:
https://wiki.alliedmods.net/Compiling_SourceMod_Plugins