Yes. You can change the size of the swap partition, by using GParted. You can install it from the Ubuntu Software Center.

Remember that gparted won't work on a mounted partition. When you are working on the swap partition, you have to unmount it first with swapoff. When you are done, to active the new swap space you do it with swapon.

NOTE: You might want to consider doing this from a live/bootable CD or USB, to be safe. Also keep in mind that anytime you deal with partitions, there is risk involved in doing so.

NOTE: When dealing with partitions, always make sure that a backup is available in case something goes wrong. You may consider Clonezilla