Universal Access is in each version of Mac OS X. If you are missing yours, then it somehow got removed by accident. If you are running 10.5, what you can do, is backup your system at least twice:
Make sure you have enough hard disk space for an archive and install:
And apply the combo update:
If you are running any other version of Mac OS X than 10.5, the instructions are different, and we'd have to know what you are running.
If that doesn't do it, you will need an archive and install:
How to Archive & Install:
and this also: