If I was asked to enter the amount of income the person who claims me as a dependent makes while filling out my own taxes, how do I change that number if it won't let me?

If you are using TurboTax Online, 

1. Go to Search in the upper right hand corner of your screen.
2. Search the term "kiddie tax"
3. On the first search result, click Jump to kiddie tax
   
    

That will take you through the section for a child with unearned income, and you can edit your entries there.