You want to make a retexture? Change the existing texture?
Anywho you can look in the entitybank\WW2 or scifi dont know which one you wanted to change?
Look up for the character open the FPE file
Its under the VISUALINFO.
textured = officer_D2.TGA or something like that.
You can replace that!
(Note that this will permantly change the FPE so its best to make a back up if you dont know what you are doing)
You can also do it like this!
Open FPSC place the character which texture you wanted to change.
Right click on it! This time its under OPTIONAL VISUALS, texture.
Click on it! And you can change the texture!
This will not overwrite the FPE! But you dont have to change it everytime you open your map. It is saved into FPSC.
And as for retexturing that certain texture.
Just do as above! Look at the textures name, open that certain texture...and you can change it!
Hope that helped!