To update to an advanced installation of IBM® XL C/C++ for Linux®, V11.1, it is recommended that you first uninstall all IBM XL C/C++ for Linux, V11.1 packages except the license package, vac.lic.
If you attempt to install a new PTF to a location where an older PTF is currently installed, the installation of the new PTF will fail due to location conflict: two files that belong to two different PTF levels cannot be installed to the same location at the same time. See Uninstalling IBM XL C/C++ for Linux, V11.1 for instructions on how to uninstall XL C/C++.
After the old packages have been uninstalled, follow the instructions in Advanced installation to install the PTF packages to the location of your choice.