Update to 5.1?

Hi everyone,

I know I am going to sound very annoying but I have googled various threads for hours and I still have not come close to an answer, so please be easy on me. I am a total noob!

So basically, Long story short, I bought this Moto G 2015 (4th Gen - Xt1072 the 5inch screen one) earlier this year, and it has been very slow ever since! So now, I am getting notifications that I cant update to 5.1!

The issue is, my phone is rooted, and I would like it to remain rooted! So, I am assuming i will not be able to install the update file.

The real question I have is, how do I go about this? How do i update to 5.1 (22.46.12.en.GB) without losing my root? I am happy with backing it all up on Titanium, and then updating but I don't know how to do it. Do I have to download the new android on my laptop and then re-install it or something? All this technical talk is literally racking my brain!

I know the solution is probably simple so I would really appreciate if someone can give me a simple answer!

Thanks so much