If you want to do it in a document class option (ie the size automatically applies to the whole document), you need to install these extra class option files. They change the body size, and they also change all the other relative sizes, so that the whole publication looks right.
Be careful to make the margins narrower if you use a small body size, otherwise it will not be readable (the eye needs shorter lines or extra spacing in order to flick back from the end of one line to the start of the next).
The defaults are actually 10/11/12 (not 10/12/14) and if you look at your log file, you'll see files like size10.clo, size11.clo, and size12.clo being used. This is because TeX was designed for books and journals, where 10/11/12 are the most common sizes: it is quite rare to use anything smaller as the body size in a book or journal, although some paperbacks do use 9pt.
If you just want to change the font size for a piece of text, not the whole document. just use the \fontsize command. This needs two arguments, the font size and the baseline distance, in points, eg \fontsize{8}{11} will set in 8pt on 11pt baselines ("8 on 11" or "8pt, 3pt leaded"). This command is documented in all the books and online manuals (eg
mine).
///Peter