To clear the swap memory on your system, you simply need to cycle off the swap. This moves all data from swap memory back into RAM. It also means that you need to be sure you have the RAM to support this operation. An easy way to do this is to run 'free -m' to see what is being used in swap and in RAM.
Check space:
# free -m
Disable swap:
# swapoff -a
Wait approx 30 sec (use free -m to see the amount of swap used/available decrease over time)
Enable swap:
# swapon -a