Error Overall budget less than overall release

I want to increases my current budget but system shows error Overall budget less than overall release .

Now my question is

   1) If I want to increases my budget then what is standard  process

                          A) if no Purchasing done under that WBS     B ) if purchasing done for that WBS

   2) If budget release then how to unrelease that budget to increase it   or Is it need to unrelease that budget to increase budget .