@xXTPlayZHDXx
get the basic programs to convert between IWI and DDS/PNG and one to edit to paste what you want like kokole's IWI to DDS converter and getPaint.NET to actually edit the images. when editing would recommend to open the original one and edit in front of it, on a new layer, and deactivate/turn off the original layer before saving.
find some places to get resources like pre-extracted textures and sounds or learn how to extract from the game and do the edits on them.