Go to Start >> Programs >> AutoDesk >> AutoCADXXXX >> Reference Manager. In reference Manager, click on Add Drawings, select all the drawings that need to have x-refs repathed. The Refernce manager will then load all the drawings and related xrefs, fonts etc. Select the x-refs you wish to repath and then hit "Edit selected paths" button, a dialogue box appears, you can either type in the path or use the browse button on the right to browse to the desired folder. Then hit the "apply changes" button.
Cheers!