[Q] (Q) Doubt about changing rom to another. topic

Hello users,

Currently I am running CM12 with Lollipop 5.0.2 in my S3.
Can someone please explain how I can change my current ROM (CM12 with Lollipop 5.0.2) and install CyanogenMod 11 with KitKat 4.4.4 ?

Please, step by step, very thanks, regards.