There is software like MSi's afterburner that allows you to overclock a GPU. Go to download.com and search for AMD overclocking software. Be advised that OEMs say that OC'ing will void your warranty. I have OC'd my SLI'd GTX 470's for over two years and no harm: but I use a non-extreme OC.
Since you have an MSI card, you'll have the most success with MSI Afterburner. Just google it, it'll be the first result. Do your research on overclocking though, because it's risky and not covered by warranty (it may even void warranty). If you've downloaded AMD's Catalyst Control Center (I'm assuming you have, just to get your drivers) you can always use it too - go to the Performance tab, under which you will find overdrive panels for both your CPU and GPU. AMD's CCC overclocking utility is very stable and dependable (and user friendly) but you will not be able to over-volt (for higher overclocks). You will need to use MSI Afterburner to over-volt if you wish to do so.
There is a lot of research you must do before you can optimize your overclocks. But basically...
1. Increase core clock in small increments, test stability with something like Furmark or demanding games
2. Continue increasing until you see artifacts or crashes/freezes
3. Research and find out a safe voltage range for your specific GPU
4. Slowly increment voltage until artifacts/crashes disappear.
5. If you reach your safe voltage limit and still see artifacts/crashes, begin to lower your core clock
6. Once you've optimized your core clock, try overclocking VRAM. Repeat steps 2-5 until you have stable VRAM clocks.
I have the MSI R7950 Twin Frozr III card myself and have been OC'ing it in the new system I built about a week ago.
Using MSI Afterburner, in settings and options turn on the option for changing core voltage and voltage monitoring.
Default my voltage was set at 1.081
Core Clock 880mhz
Mem Clock 1200mhz
I have OC'd to 1100 Mhz / 1350 mhz @ 1.100 Voltage and has been stable playing games, and in windows, and running the Unigine Heaven 3.0 benchmark.
Playing games my temps hover around 64-66C doing a benchmark or other "stress" test it goes upto as much as 69-71C and the fan becomes audible...
So far I am very satisfied with the card.
One thing to note, I thought I had a bad card when I first tried overclocking and saw artifacts in a game... However I determined that GPU-Z was the cause...
If I have GPUZ open on my 2nd monitor with the setting "Refresh GPUZ even when in background" then sometimes when playing games weird artifacts and graphical glitches appear evne when the card is at Stock settings.... closing GPUZ or just unchecking the box for refreshing GPUZ when in background makes the artifacts go away... Once I determined this and was confident the monitoring temps/voltages in MSI Afterburner were within 1% of what GPUZ was showing I stopped using GPUZ due to this issue....