I’m assuming that you’re reading this because you have used a previous version of Ultima III — you can simply drag your “Roster” file from any older version of Ultima III into your Ultima III 1.3 folder to preserve your game(s)-in-progress. Running the patch to upgrade from 1.2 to 1.3 preserves your registration information.
Even if you’re familiar with a previous version of Ultima III, I’d still suggest skimming through the “Read Me First” file for additional tidbits. What is listed here is just a summary of changes to Ultima III since version 1.2. The “Option:” items listed below are accessible from the “Custom Settings…” command in the “Options” menu.
∞ Option: Save only when asked.
∞ Option: Simple Automatic combat.
∞ Option: Move diagonally.
∞ Option: Ignore wind.
∞ Option: Play sounds asynchronously.
∞ Different map size support.
∞ Party is now optionally resurrected when the last character dies.
∞ Abort to Main Menu command added.
∞ Easier character creation.
∞ Detects when a font will conflict with the one built into Ultima III.
∞ Detects when an old version of Speech Manager (<1.3) is in use.
∞ Keeps the ctSeeds smashed (keeps graphics fast after update events).
∞ Handles update events when peering at gems.
∞ Handles updates better on low-res Macs.
∞ Ztats shows the correct player icon again (broken in 1.2).
∞ Allow use of numeric keypad for movement in dungeons.
∞ Other small refinements too small and varied to mention.