It's an alright PSU, however number 1 rule of having a pc is having a quality PSU or else things can go wrong real fast for you, i recommend in the future to upgrade it to prevent any issues as that CS550M won't last forever (it's not the best quality)
Here's the list
https://linustechtips.com/main/topic/1045610-new-psu-tier-list/
Lower tier = worse, higher tier = better
Rule : Don't cheap out on your PSU ever, or you'll regret it.
As for your GPU, you don't need to upgrade depending on what games you play, if it's fortnite, minecraft e.t.c then no you don't need to, if you want to go more high end (witcher, skyrim, ghost wildlands, e.t.c) then you need a new one for sure.
I will refer you to
https://www.umart.com.au/Asus-ROG-Radeon-RX-580-Strix-Gaming-8GB-Graphics-Card_38812G.html as it's a great GPU and it'll be able to run everything you'll need for the forseeable future.
However before you upgrade you might want to consider getting a new PSU, you don't want yours breaking on you anytime soon and having it destroy your graphics card, nevertheless it's entirely your choice.
k good luck with whatever you do and remember when building or replacing parts use A : anti-static wrist band to prevent static electricity or B: touch your case every few minutes to relieve static off yourself, one discharge to any component and it could destroy them and in some cases it can happen over time slowly not immediately.