common5.pac > sc_selcharacter > char_bust_tex_Lz77 and all the MiscDatas you see in there are the CSPs for character. Go into any MiscData and click any of the files to see a preview of what CSP it is, then to replace it just open an image up in any image editing program, resize it to the same dimensions as the CSP in BrawlBox, save it as a .png, then replace the one in BrawlBox with it.
You should follow
this guide for a more thorough explanation.