How much swap do you have now and how much is presently being used? Post the output of the free command.
If your present swap is not being maxed out then adding more will not help. To add additional swap if you have some unallocated drive space you can create another swap partition.
Then use the mkswap command to format it and then swapon command to enable it.
mkswap /dev/hdxy (replace xy with drive and partition id)
If you do not have any unallocated space on the drive then you can create a swap file. It will not be as fast as a partition but you can see how additional swap will effect your system.
What services are you running? Shutting down services that you do not need will help speed things up.