The cooling system in the laptop is probably not quite adequate. There are some things you can do to help circumvent this problem, but there's a possibility it's just the result of poor design on Acer's end.
Things you can try:
» Laptop chill pad. Look into the Notepal series from Coolermaster
» Thermal compound. The laptop will need to be opened and the heat sinks removed to apply new compound (If this will void any warranty you have, that's at your discretion!). Using something like IC Diamond or Gelid GC Extreme can reduce temps.
» Make sure the vents have room to actually ventilate the hot air (i.e. don't set the laptop on bedsheets or anything that will retain heat, and allow space around the laptop for heat to dissipate).
» Again, this suggestion may risk your warranty if you're still covered: some enthusiasts like applying copper RAM heatsinks to the CPU + GPU heatsinks/heatpipes. It doesn't make a huge difference, but every little bit helps - especially if you're taxing the system heavily.