I want to get more data but don't know how
As noted, go to your account page. The option to buy more will be there if your plan supports buying more - not all plans provide a buy more option (for example unlimited plans at last check do not). $10 per GB. I believe the Viasat app also supports the buy more option if applicable to your plan.
With the new world of Streaming will Viasat be offering a better plan with more data any time soon, it sickens me to pay the high rent for Data when my Son gets Cable internet in town for 19.95 a month, Rual area's are being taken advantage of because we don't have other choice's, we all need to right a letter to Congress for fair pricing