Arch Linux

Install pacman-contrib, this gives you access to pacdiff which goes through all your pacnew files allowing you to see diffs of the changes and giving you different options to deal with them.

Now my question is, how should I deal with these pacnew files? should I always remove them, always replace them, always read them and decide?

Always read them and decide what to do. However, what to do usually isn't too remove or replace them, but to update them with the changes instead. Most text editors have a way of looking at a diff of two files. This will highlight the differences and you can decide based on the individual changes (maybe it's something you purposefully changed, maybe it's a change to the default). If you use vim, vimdiff will do this.

I'd rather not read these things everyday, it's a bit boring, so I hope there's a better solution. How do you deal with these?

After you make your decisions on what to do, delete the pacnew, otherwise you'll keep getting messages about it. They don't get updated all that often (except mirrorlist, I usually just delete that and run reflector every once in a while).

EoS has a graphical welcome app with a pacdifmeld menu item, so click on that and get reading. However if you are a beginner and have not modified system files manually, overwriting the old file is usually a safe option.