Hi
Normally Options is under the Tools tab on the top toolbar.
As I discovered recently though, Options may not be visible on the "Home" toolbar beneath this as It depends on your screen resolution. (Mine is 1024 x 768.....anything higher and everything is a bit too small B)). If you can't see it in the "Home" toolbar you should see a double chevron at the right hand end of the bar. Clicking this will show any extra options which should include Options
If this is the case but you want it permanently visible then set up your own toolbar with the Custom and Customize option.
You can use a setting under Options/Disk to limit the cache size.
Nat