How do I upgrade my skills,nothing works,all it lets me do is skill training but never skill upgrades,so I’m at level 1 on all my skills on all 3 of my characters?

Farm skill books. In the desert or field of valor you gain good skill books or certain maps where skill books rate drop is higher

How do I get my skill upgrades done? I get a lot of skills that need upgrades and I have no idea how to do it! Please someone help here here!!!!!!!