Running Windows 98 & RAM not recovered

My PC is running Windows 98 on a Compaq 400 mhz 64 meg RAM machine. Presently after being rebooted, I have 72% memory available. After surfing the web or running games or other applications, the available memory will decress. After awhile I will go below 50%. This will never recover unless I reboot, which seems to be often since surfing the web starts having problems. I can increase memory, but is there anything I can do to recover memory except for rebooting.