If you're rooted, do as the previous poster says, then delete the default one, this is what I did benefits are I really like smartkeyboard pro and I save some internal space.
I think I understand question and had same problem. Was long pressing screen and couldn't figure out how to change to Smart Keyboard Pro. Finally saw a tiny icon of a keyboard in the notification area at top of screen.
Pull down the notifications and you change it there. New to Jelly Bean LOL.
I installed gokeyboard and hated it and uninstalled it and now no matter what keyboard I install and activate my phone stays with the android keyboard... I've tried every method here including long pressing the globe key on my keyboard and picking it from the system menu and from the pull down menu.... Nothing works... Please help