1. Call Garmin (800-800-1020) and ask for sales or tech support (and don't be surprised if one transfers you to the other...)

2. Tell them you want to upgrade.  They will ask you for the serial number of your G3 and a credit card number (there is a charge of $100 to upgrade + tax several states).  If you want to order one of the MapSource CD's, you need to tell them that too (about $100 for the US Roads and Recreation, and $70 for the World.  The Topographic one isn't out yet...)

3.  They'll give you an RMA number and instructions for returning your G3.

4.  Send them your G3 and wait for them to send you a G3+.  (Turn around time seems to have been from 1 to 5 weeks, probably depending on when they get a shipment of G3+'s.)

5.  This is for the US only.  Anywhere else, call Garmin and ask 'em how/if.

"Please note that the GPSIII to III+ upgrade program will end May 31st, 1999 and units must be received no later than June 15th.  Please call GARMIN for a Return Authorization number if you would like to participate in this program."

Garmin Technical Support