new software for xiaomi Mi 5s Mi5s 5.15 inch

[stefanDB]

here is a link to the page where I bought the phone: https://www.banggood.com/Xiaomi-Mi-5s-Mi5s-5_15-inch-Fingerprint-3GB-RAM-64GB-ROM-Snapdragon-821-Quad-Core-4G-Smartphone-p-1091260.html?rmmds=search

So I have this phone now and I would like to install a mostly vanilla version of android, but I am a little bit hesitant. the software that is currently on it is functional but not very good. since the phone is new I don't have any personal data on it or something, so the only reason to make a backup would be to repair it if I fuck up. 

I have never done anything like this before, so I would like to know how big the risk is and what is the best way to do it. does anyone have a good guide on how to install a custom ROM, and which steps are not necessairy if you don't need to backup any personal data? 

also, where can I find how to unlock the bootloader on this specific phone?

[clickme.sh]

This should help you out, https://download.lineageos.org/capricorn Official Lineage OS nightly Builds.