What do you need to upgrade? What is wrong with the bike? Pedals yes that is usually a given because if a bike comes with pedals they are usually cheap test ride pedals. In terms of seat posts those are generally going to be quite hard so it holds up, some do have some built in flex and some are mechanically softened from springs or elastomers or something.

If you are referring to your saddle that probably isn't necessarily wrong it might just not be adjusted for you, it could be the wrong saddle but the only way you will know is after you take time to ride it some distance and get used to it and also make sure it is adjusted for you which is always easiest done with the help of a professional fitter.

I mean generally I wouldn't do much upgrading on a new bike beyond some touch points and just get the bike I wanted in the first place. The bike you got is decently spec'd and in general unless you have specific issues that have arose from your fit I would just ride it for a while get used to it and get a feeling of what you like and dislike and then move on from there.

If you are a chronic upgrader you would a be a good candidate for building a bike from the frame up or going to a custom frame builder and doing that. That is generally what I have done for almost all of my bikes save for one only because I couldn't get it fully custom built due to restrictions on some of the parts and the frame materials and the builders and me not wanting to go way way way over the top. However that was an e-bike and there were things I wanted that couldn't be done without some craziness and I am super happy with what I got and the maybe silly upgrades I did.