Data

Yes, you will lose the rollover if you change your plan.

You will lose your rollover.  If you are not using enough data to keep a 25 gig plan you might price if cutting your data plan will save you money.

Any change in your data plan will cause your existing rollover to be wiped clear, no matter if you are increasing or decreasing your data plan.

Liz is correct,  you should seriously evaluate your needs and get the data plan that is most appropriate for your needs.  If you use 20GB of data once a year, and only use 5GB the rest of the year,  then you might be far better off to get a 6GB (or similar) data plan and save $50-75 each month, then that one month you need 20GB,  spend the $225 in overage charges, but you are still saving about $225 total over the whole year ($50/month for 11 months minus the one time $225 in overage)

@GeekBoy is right. I have a 3 GB plan and increase it to 16 when we go to Florida and I am tethering two laptops. Then drop it back to the 3GB when we return.

@GeekBoy Any change they make now will result in one of the new plans that have no overages. The only option they will have for when they need more high speed data is to switch to a higher data plan.