install Nexus S custom ROM?

HI everybody

I need help!

I have a Nexus S running android 4.1.2 Kernel 3.0.31 and I want to install a Kernel and ROM that improves the phone, I want performance, I don't care about fancy options, I'm not planing to use my phone for anything more than the simple stuff, but as it is right now is terrible, freezes all the time, sometimes doesn't respond, well is just a mess.

I already try all the possible options fro a normal user and now I want to go further rooting it

If someone can please tell me what's the better ROM and Kernel for an optimal performance will be so much appreciate it, I'm not a computer guy and my knowledge of this is 0, my intention is just follow a tutorial and hope my phone survives.

Thanks in advance.