Go to the Cache Configuration, Garbage Collection Settings form.
Check Enable garbage collection
Fill in the following fields:
Set Low Water Mark - must be lower than the High Water Mark and
is not usually set below 40%
Set High Water Mark - must be greater than the Low Water Mark,
less than 95%, and greater than 50%
Cache algorithm to use
Click Submit to update your server with the changes you made to the form or
Click Reset to return to the values that were on the
form before you made the changes.