The Choosing a larger education credit screen-529 plan

Hello,

 

I'm trying to understand the concept of this screen as it is suggesting I can enter a value between $0 and 4000 to help reduce my taxes.  I'm a little concerned of doing this wrong, and also if it is 0-4000, why is TT showing a larger amount ($8,862) in the first place?

I'm looking for any help in understanding the concept behind this and where the numbers come from so I can feel more comfortable about it!