Help me to use the GS7 please

Hello guys. My father bought me a GS7. It was Verizon but theres no sim lock. I have lots of problems. For ex when i restart my phone it forgets all wifi hotspots. Becouse Im using different carrier i cant update my phone. Please help me to fix this issues without losing simunlock. New rom root, I'll do everything about it. I need solutions please. My phone also freezing sometimes

Please help. Sorry for my bad english. Please help :(:(:(:(