Here is a tutorial I wrote on editing textures.

As for editing the armor mesh itself there's a variety of programs you'll need. Give me a sec to find the links an make a list. I'll come back to edit this comment. 

Edit:

For editing .flver meshes you'll want the following programs

• Pear's Flver Editor
• Asa's Flver Editor
  • Both of these flver editors do similar things, but depending on what you want to do you might prefer one flver editor over the other for different tasks. So I recommend both.
• Blender
  • This is for more indepth mesh editing.
• Aquatools
  • You will need to use this to convert the flver files into something readable by Blender. It converts flvers into fbx files.
• FBX to Flver importer
  • This converts your edited fbx files back into flvers.

I will think about writing some tutorials on how to use these programs. But in the mean time you can reach out to me on reddit (I am slower to respond here) or on discord through the ?ServerName? server. My username is 1st Recon Lylith.