Giving up on Knox 0x0

Hi,

my warranty ran out and now I do not care about keeping knox 0x0 anymore.
I would like to install the most clean android version on my cell and keep the
stock os aswell.

1. How do I do that?

2. What is the best recovery?

My Phone: SM-N9005
Android: 5.0
Baseband: N9005XXUGBOA1
Kernel Version: 3.4.0-3643614
Build Number: LRX21V.N9005XXUGBOA5

Also since updating to 5.0 with mobile odin my cell keeps rebooting itself several times a day by itself.
It has nothing to do with the battery. I think that while updating I kept my old baseband and thats causing
these issues.

3. How do I fix that?


Thanks