Automationbabe has told you how to create new dimensions without brackets. I recommend this too, since I use the reference dimensioning feature to apply real dimensions.
To remove brackets from the existing dimension, right click on the dimension and select properties. Deselect "Display with parentheses".
Open a new drawing, part, or assembly, do as Automationbabe has suggested. Then save the drawing, part, or assembly as a Template. So you don't have to set that option every time.