Change the working units with Tools + Options + Units and Parameters. Set the units to Length to inches. You don't need admin rights to do this. The units you select are for your use only and they are not saved with the CATIA file.
Change the dimension units from within the Drafting Workbench. In the Dimension Properties toolbar, change the style form NUM.DIMM to NUM.DINC You don't need admin rights to make this change either.
I believe Ferdo's link tells you how to reset the default dimensioning style. You will need admin rights to do this.