Default [Q] Rooted, with 4.1.2 MB1 - but want 4.4.2?

As the title says, i've got a s3 that I haven't been using for awhile as I also have the S4, but may want to sell the S4 and go back to the S3 just to raise some funds. I've also got TWRP installed, but don't know what version, I think i's the latest, but not sure. What do I have to do to install a 4.4.2 rom or even factory image - I really don't mind TW?
Thanks,