Modding HD textures into ME1: How hard is it?

Hi, I wanted to ask something concerning modding ME1. I wanted to try adding in HD textures, mainly for the character models. How hard is it to do that? I saw a program called me3explorer mentioned, but I don't know how to use it. Is it difficult to use or fairly simple? I've also seen texmod mentioned as well, what is that exactly and how does it work? Thanks in advance.