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The 'limit' on the i5-2410M is listed as 16GB and Memory Types DDR3-1066/1333 - http://ark.intel.com/products/52224/Intel-Core-i5-2410M-Processor-(3M-Cache-up-to-2_90-GHz)
So as long as Acer didn't do something stupid you'll need a 2x8GB kit, but as far as 'speeding' things up oddly often the opposite is true in some situations and that's waking, sleeping and hibernation. I assume it has a 64-bit version of Windows to access >4GB of RAM.
To speed things up the number 1 thing to 'buy' is an SSD, by far the slowest thing is your mechanical HDD.
Q - Why do you feel 16GB is needed?