To be clear, these are the hotspot data plans which all include unlimited mobile data, then give you a certain amount of hotspot data for a price. The new set of plans puts the 500MB, which had cost $20, as the free option, and when that 500MB limit is reached it will direct users to the 2.5GB plan, which now moves into the $20 slot. If you already have one of the more expensive plans, you'll simply get more data to use. If you currently have the 2.5GB plan, you'll be bumped to 4.5GB and still pay $30; and, those with the 4.5GB plan will now be getting 6.5GB and still pay $40.
The new plans have already gone into effect, but if you are on the 2.5GB or 4.5GB tiers, you won't be migrated to the new plans until this Saturday September 14th.