My wife has just got a Kindle fire HD tablet and have been trying to work out how to add her own wallpaper and screensaver.

But we have been having trouble finding out how to do and even if you can as it does not seem to have its own ones to install.

Can anyone please help with this please?

This is the first result of your question on Google. There are many others:
http://www.lovemyfire.com/change-kin...wallpaper.html