Low memory is essentially insufficient Random Access Memory, to alleviate the issue, double tap home, hold app icons till they jiggle and hit the minus sign to free up RAM.
An iPad 2 has 512MB of RAM.
You can download utilities like Memory Doctor Lite or Pro at $1, hit the optimise option to free up RAM in seconds if multiple attempts on quitting all apps dont free up memory. However, there are issues where the optimise button doesn't work, so test out the trial. The trial works for about 2-3 uses.