Hardware Upgrading

It is pretty easy to be honest, but some things are easier than others.

RAM, Graphics Card, Hard disk are fairly easy.

Power Supply, Motherboard, CPU are a bit trickier.

Just be weary of upgrading your graphics card beyond the limits of your power supply.

If i was to upgrade the graphics card would other components need to be upgraded in order for it to work?

Possibly the power supply, depending on how chunky the graphics card is and what wattage the power supply is.

Admins.

I would think if you buy a half decent gfx card you will need to upgrade you PSU.

If you can spend the money I would change the PSU anyways as unless stated it was a good brand of PSU it is very likely that you have a cheap piece of carp, that if you put any stress on the system can potentially fry the mobo. Can you give us a model and/or specs of your system and i will give you as much advise as i can.

Good sites to order stuff from are:
ebuyer
scan (even more so if you live in the north-west near Manchester/Bolton)
dabs
overclockers

As far as what cards to buy i would suggest the following:

Amd 7770 - this is entrance level and will give you overal quite good performance on med-high settings on most games and good frame rate on med settings on games like BF3. Will set you back just under 100 quid.

AMD 7870/Nvidia 660 (NOT ti) based on what you have said this is prob the highest you would want to go at the moment. Very good performance vs pound. You will be able to play most games on High - Ultra. Just shy of 200 quid.

At this moment i would tell you to get a 7770 - wont dent the budget too much, should work even on the cheap piece of carp you have as a PSU (though I would still tell you to replace it regardless), it wont put out too much heat (i would also guess that your case hasnt got too much ventilation) and is prob the best Pound vs performance you will find.