It depends really on what you do with your computer, do you game? do you watch videos? what games do you play? etc.
I'm gonna assume you go for gaming. For this I'd suggest you upgrade to a discrete graphics card, such as a HD7770 or the equivalent R7 series GPU (I believe it's the 260.)
This'd probably be the best cost-worthy upgrade you could do. Thought as many will suggest a full upgrade will be necessary to get optimal performance on the newest titles.
We need a lot more info to really give good advice.
First of all for gaming - is there an existing graphics card in the system (not onboard graphics)?
Besides that - the games you want to play, resolution, and budget are all helpful.
That said - if your budget is over say $800 - You will want to start over from scratch. A budget of under $400 id suggest GPU (depending what you have now) and SSD. Between $400 and ~$800 I'd suggest you save up to do a full system replacement.
with 200 euros you should be fine going for a mid-end Graphics card.
With this budget, I'd suggest going for the GTX 750ti or the AMD 7850 (or it's R7/R9 equivalent), but ultimately you should be considering upgrading to a new system.