How to modify a tolerance of dimension？

In a drawing，I want to modify a tolerance of dimension，the dimension was selected in a dimension style。

The first attempt failed, the second was successful。Must modify the tolerance again，then the tolerance is new。

How can  successfully modify tolerance at fist time。

May be there is a bug in solidworks。

I find a quickly way to change the tolerance。

first modify the style of dimension to none，then  modify the tolerance was  successful。

I don't know why direct modify the tolerances was failed。