MSI Afterburner and Kombustor are used for GPU overclocking.
Perform a slow increase in the core and memory clock by intervals of 5, then running Kombustor's GPU burn in for a few minutes. Continue increasing by 5 until Kombustor's burn in causes the GPU driver to crash. Then reduce the clock by 10~15, and run the GPU burn in for 3 hours to ensure it runs perfectly stable.
Keep temperatures below 80'C at 100% load, whatever happens first.
CPU overclocking is something you'd want a closed circuit cooling loop for, which is something I highly doubt they put in a retail computer.
Edit: Do not overclock if you intend to return the system to buy the parts and assemble it yourself.
Putting a system together yourself is always going to be cheaper. Do note that you will need a closed circuit cooling loop
for your CPU. They will run you $60~$80.