If you still have access to your mobile phone:
If you still have access to your mobile phone you can simply go to Settings > Account Info and click on "Change" next to your phone number. Your phone change will be processed instantly.
If you lost your phone or no longer have access to the Authy app:
Open https://www.authy.com/phones/change on your browser and enter your new and old phone numbers.
Note: Phone changes require additional security checks and will be processed between 48 to 72 hours.
If we find unusual information in your request, we might ask for your ID and other questions regarding your usage of Authy to verify your identity and ownership of the project.