Elf is just an binary-format. To 'edit' that you'll need some software which is capable of disassembling that binary.
Popular choices for that are: IDA, radare2, hopper disassembler and binary ninja.
Though judging by your post you're still very inexperienced with this stuff so you're unfortunately unlikely to achieve whatever you're trying to change unless it's something really simple.
If you don't plan on modding the executable of the game but rather the resources (images, sounds, maps etc.) then you want to mod the romfs, not the exefs.