64MB is the default memory limit for Java, but it is easy to change:

1. Unix: edit the jas script used to run JAS and on the last line insert -Xmx128m after ${JAVA} (This should be made easier JAS-328@BUGS)
2. Windows: Edit the file jas.ini (typically c:\Program Files\JAS3\jas.ini) and uncomment the line: --Xmx128m
3. MacOSX: There must be a way but I don't know what it is. Ask again if you need it.

Of course you can replace 128 with however many Megabytes you want JAS to use (but make it < the actual physical memory you have on your system or the program will page like crazy).