how to increase RAM for garageband?

i constantly get this message: 'couldnt insert or delete data, out of memory', until it goes away i cant do any work. I have 16G ram and more than enough space on my harddrive. i found a temp solution which was the change the input/output sound on garageband preferences. then the error started to come back. im trying this solution now: http://support.apple.com/kb/ta25701?viewlocale=en_us but im not able to locate the 'change memory for application' section. how can i change the RAM settings for garageband? its really frustrating that i cnt do my work simply because of this. is there any way i can change this? and usually on my activity monitor, it shows that garageband runs on a maximum of 2G ram. ram is clearly not the issue because i have more than enough. thanks so much