You will need to download TXD Workshop from here: http://www.thegtaplace.com/downloads/f7 ... rkshop-40b
Once you have installed TXD Workshop, you will need a mod to install. Once you have a mod (either skin or vehicle)
Go on the TXD Workshop program and click "Open IMG"
Navigate your way to your GTA SA dictionary. Once found go to the "SAMP" folder and click "SAMP.img"
Now click on "Action" and then "Add" then navigate your way to the mod .txd and .dff you have just downloaded.
Once you have opened the .dff and .txd hit "File >> Save" and you have sucsefully installed the mod.
the SAMP.img will overlap your GTA.img file so you'll need to install SA-MP if you want a fresh non-modded GTA.
Open TXD Workshop then navigate your way to GTA SA folder and click "SAMP >> SAMP.img"
Find the mod you want deleted (.txd and .dff) and delete them.
Save the file.
Credits to Shadow