Following invitations heading out to developers, Google has now been sending invitations to existing Glass Explorers, offering them an updated unit in exchange for their current product. Owners aren't required to make the swap, of course, but doing so will bring about some welcomed changes, not the least of which is the ability to use Glass with prescriptions glasses.
Those who receive the invitation will have until February 5 to make up their mind, at which point the one-time offer expires and they'll presumably have to wait until the next upgrade period. The updated Glass units are still Explorer Editions, and are necessary to take advantage of some accessories and features that will be coming out in the upcoming months.
If you weren't completely enthused with your Glass's color or you want to give a new style a try, you can select a different color option than your original one. In order to swap, owners have to fill out the form received with the invitation, which pegs one a slot in the waiting list, something Google says is first-come, first-serve based on color. Translation: don't delay getting your request in.
Once the new unit is available, Google will then ship you a return box for your original pair (shipping label included), and you'll have to wait about a week to get your new pair. Google says it will take 3 to 5 days after the original pair is received for the new pair to be delivered. Rounding it all out is a promise from Google that "your old Glass [will be] duly honored when you send it back. Stay tuned..."