Google is asking Google Glass Explorers - those taking part in the wearable's beta program - to swap their first-generation Glass model for the updated version.

An email was sent on Wednesday to the participants who originally shelled out $1,500 to get an early look at the new Google Glass. They don't have to swap their pair, but Google says "we think you should".

The new Glass that will be sent to customers is still part of the Explorer Edition, and doesn't differ too far from the first generation.

"It looks the same. It feels the same," Google writes. "But there are some subtle improvements." The Glass team has added extra durability, compatibility with upcoming prescription frames, and the ability work with the new Shades and mono earbud accessories.

"Simply send us your device, and we'll replace it with a brand new Glass," Google adds.

The offer to exchange your first-generation Glass for the newer one will expire on 5 February 2014. Explorers have been given access to a website where they choose a colour for the new model.

Explorers don't get to keep their first-generation hardware - they must send it off to Google. But the company says it has something "special" planned for the old parts.

Don't have $1,500 for the Explorer program? Google has confirmed it will be launching a consumer version of Glass at a cheaper price and with wider availability in 2014. The second-generation Glass for testing is a step in the right direction.