If you update using a patch you will retain any files you added (shirts, rackets) etc. but will lose any original files you modified. Just make sure that you back up any files that you have changed.
When I last updated I backed up:
You may have more (menu .jpg's, original stadia/courts replaced etc.)
Even if pasting the files doesn't work, you can always paste the relevant parts back onto the new files, there probably aren't too many.
Link to patch is here: http://www.managames.com/Forum/topic15-4450.php
Remember if you have a very old build you can't use it. Also if you extracted your files from the PAKs you will need to do it again after patching (or the game will not run).