There is no problem to continue using the Office already installed. In order to install Office provided by the University of Tsukuba, you need to uninstall the existing Office. These tasks must be done at your own risk, and the University of Tsukuba does not support it.
If you use Office provided by Tsukuba University, you can always use the latest version. In this sense, decide for yourself whether to use the Office already possessed or the Office provided by the University of Tsukuba.
If the Office you already have is no longer supported, please use the Office provided by the University of Tsukuba.