How change dimension in Toolbox component. always "read only file"

You need to create a 'custom profile'. The help system should tell you how to do this.

But i want to do it with Toolbox profile. So it is not possible?

After you have created the weldment.
Expand the structural member component
Open the sketch
Modify as required
You are done
This does not alter the weldment profile in Solidworks and you can reload and revert back anytime