I have the Simple Choice plan with 2gb per line. When I check my plans and services tab and look at my data service it says i have 1gb high speed data. When I go to the Manage Data and Add-ons page it has an option for 2gb high speed data, which says its free, if I choose that option it wont change anything about my plan will it? Just give my phone 2gb high speed instead of 1gb, since I assume im paying for the 2gb plan and it was just set to 1gb on my phone as default. Might seem like a stupid question, but I want to make sure by changing settings I'm not messing with my plan or how much I'm charged.
You are right that the 1GB was mostly likely just placed there by default when the line was initiated. You can change it over to 2GB without any ill effects to your Simple Choice plan.
Manage your T-Mobile account