What to upgrade ?

R9270. You will see a much bigger improvement right now.

Then again, it depends on what you use your PC for. For gaming, upgrade the GPU first. If all you do is video editing or music production, then the CPU.
 
RAM:8gb
Graphics card:R9 270
CPU:i5-4430
PSU:630 Watts
Windows 8.1
I'm looking to play Arma 3 multiplayer (not on max settings), and basically investing in new equipment for the future, when new games get realesed, so I can play high-ultra settings 1080p and my budget is around 200-260 euros (217-282 dollars).
 


I would definitely upgrade the GPU. Your CPU should be fine.
Try this R9380 from MSI:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127878&cm_re=r9_380-_-14-127-878-_-Product

You could also get a GTX 960 for that price range.

If you're willing to add a few more to the budget, you would be way better off saving for a R9390 or 390x. They would be more suited for the next couple years.
 

Where I live there's ASUS Radeon R9 380X for sale 10% off, and it costs 260 euros, and btw I don't really have an ability to buy stuff online, because I'm only 15 years old,and my parents are not really into that stuff, lol.
 


Well I would go for the R9 380X then. It should do just fine.
 


Ok, thanks for your help! :)