Recommendations to improve current rig

[kingrocky]

Last Christmas i bought a pre-built pc... not the best idea in the world but thats not what i need help with

i have
Intel Core I5-2320 CPU @ 3.00GHz (can be overclocked to 3.3GHz) (Quad Core)

AMD Radeon HD 6670 2GB

8 GB Ram (2 & 4GB)

1.35 TB of Disk space

Foxconn H61MXL/H61MXL-K Motherboard

Windows 7 Ultimate

It is very similar to http://www.pcworld.co.uk/gbuk/advent-dt2111-desktop-pc-11875804-pdt.html

i got it from pc world, since then i have realized my mistakes about pre-built computers, furthermore i would like to improve it so it plays games such as Skyrim and Day-z upon higher settings, i have considered getting a new graphics card but im not sure as i may need a stronger power supply, apologies for Poor Knowledge upon this matter and this is why i have called for help

I have around £250 to spend on improvements
I'f you need anymore information i'll gladly try and answer for you.

Thanks for reading and any recommendations will be greatly appreciated

Michael,

 

[kingrocky]

The Ram is DDR3 and Dual Channel

 

[benitopsp]

Buy a 500 Watt PSU and the HIS Radeon 7770.

 

[Wolfshadw]

Buy a 500 Watt PSU and the HIS Radeon 7770.

Correction: Buy a quality 500 Watt PSU and the HIS Radeon 7770.

-Wolf sends