If you need the relative location to be changed, you can modify the .xml file in the <project_name>.data/source_x folder by following the steps below:
1) Modify the following line for each source file:
2) Change the path to match the new relative location of the source files. The $PPRDIR is the current location of the .xpr file.
You will need to reopen the Vivado project after changing the .xml file.