how do i increase my allowable mail amount on icloud?

The space for mail is part of the overall space, which at the basic free level is 5GB. You can increase the storage at a cost: additional 10GB, $20 p.a., 20 GB, $40 p.a., 50GB $100 p.a. It's up to you how much of your space is used for email and how much for other things.

To purchase extra space see this page:

http://help.apple.com/icloud/#mmd602084a

and expand 'Purchase additional iCloud storage'.

What does System Preferences>iCloud say about how much storage you have? If you are having a problem over this you probably need to contact Support: http://www.apple.com/support/icloud/contact/

Then it doesn't sound as though you have more than 5 GB of icloud storage.