Upgrading & removing bloat from unlocked AT&T Galaxy S4

[dheian]

Inherited an AT&T-branded Galaxy S4 and received an official unlock code from AT&T as I will be using a Canadian carrier. The phone has the usual bloatware and is stuck on 4.4.4. Would love a pointer to upgrade articles or what my options are with this model. If I understand correctly, I may not be able to go to something like Cyanogenmod due to a possible locked bootloader? Thanks.