Board Thread:Skyrim/@comment-12182749-20130821174008/@comment-6881629-20130821183543

I asked her to mine some ore for me once... she said no. Faendal will though.

To upgrade a followers armor or weapons just give it them to carry it (there's a dialogue option) if its better than what they have they'll equip it. Some very rarely change their bows though (its a bug).