Currently, you cannot change the vote allocation for Aha! users within the Account > Billing settings as votes and vote limits are restricted to and only apply in the portal.
Some of our Aha! users are also users of the Ideas Portal; however, we'd like to increase their vote allocation given their role. It is possible to increase the number of allowable votes by editing a Portal User and increasing their vote allocation. However, this is not an option for Aha! users.