How to increase swap memory in OS X?
Swap is issued only when needed. There is no limit so if you have a memory leak, that will crash a program or allocate swap to grow as needed.
Usually the kernel detects and protects you, but worst case, reboot and swap is cleaned each restart.
How are you measuring things to conclude “swap memory is fullest”? It starts empty and grows as you use the system and then cleans each reboot. What value is swap now?