you may use this software "changename" from Colin Mulliner
http://www.mulliner.org/palm/
or you may also do it manually,
1. Open the Memo Pad application on your handheld.
2. Tap New.
3. Enter the ShortCut character. (capital "S" -> ALT)
4. Enter a period '.'
5. Enter the number 5.
Whether you entered the shortcut character, period and 5 correctly or not, the characters you've entered will disappear and the memo pad will remain blank.
If this is successful, then you will not find your username on the upper left corner of your screen (go in the Hotsync application, first)
Hope this helps