Idle at 70C is pretty high - I imagine the fan or fans are going at full speed all the time?
First thing I would do is give a thorough cleaning - remove the back plate and use canned air and a vacuum hose to clear out as much dust as possible. Use a q-tip to get the hard-to-reach places. Pay special attention to the heat-sink cooling fins, the fan intake filters and fan blades.
If that doesn't cool it down sufficiently, it may need a reapplication of thermal paste. The stock thermal paste applications for OEM laptops usually suck any way, and if it's more than two or three years old, it's probably overdue.