Help with removing sleeves

Hi. It is not. What you need to do depends on what the mesh you want to edit looks like. If the sleeves are texture-based, you just need to edit the textures. If there are sculpted details in the sleeve area, just delete and replace the arms.

All of it should be covered in the frankenmeshing tutorials. Here we do not write beginner-oriented tutorials because we would need to explain how to navigate three software as well.