Low Profile Card-or Case upgrade?

[Guggs]

Hey guys, my dad bought a micro imedia PC a while back for general use that could do a little bit of gaming. I been reading a little and apparently my motherboard is a mATX type, is that right? But the graphics card isn't really amazing and I want to upgrade it. So what would be a better option? To buy a low profile graphics card and install that or buy a new bigger case and a normal sized graphics card? And please recommend which of either would work out better and what type of case or graphics card I should buy? Any help would be appreciated thanks.

Current System specs:
Model: Packard Bell imedia s3210
Current Graphics card: Radeon HD 4350
Motherboard: WMCP78M
Budget: £120 maybe push it to £140.

 

[Guggs]

I have a 250watt psu currently, but i understand with a graphics card upgrade i will have to buy another psu. I currently have a 400watt one lying around so can use that if power supply consumption is lower than so. And thanks