Why can't I change my homescreen or lockscreen?

[AC Question]

When I try to change my wallpaper and I click on the gallery option, it always says "app not installed". It only let's me use google's default wallpapers. I can always change my homescreen when I download a new launcher, but the launcher never allows me to change my lockscreen. I've tried to fix this for days but nothing works, can someone
please help me?

 

[Tim1954]

Can you do it from within the gallery app? Open the pic you want to use and click on "more", that should give you the option to use the pic as wallpaper.... Good luck