LaTeX.cls files can be accessed system-wide when they are placed in the <texmf>/tex/latex directory, where <texmf> is the root directory of the user’s TEX installation. On systems that have a local texmf tree <texmflocal>, which may be named texmf-local or localtexmf, it may be advisable to install packages in <texmflocal>, rather than <texmf> as the contents of the former, unlike that of the latter, are preserved after the LATEX system is reinstalled and/or upgraded.
It is recommended that the user create a subdirectory <texmf>/tex/latex/CUED for all CUED related LATEX class and package files. On some LATEX systems, the directory look-up tables will need to be refreshed after making additions or deletions to the system files. For TEXLive systems this is accomplished via executing texhash as root. MIKTEXusers can run initexmf -u to accomplish the same thing.
Users not willing or able to install the files system-wide can install them in their personal directories, but will then have to provide the path (full or relative) in addition to the filename when referring to them in LATEX.