Didn't see an option for this and would like to upgrade remote P2s. Upgraded local via VSC.
Upgrading P2s to 6.3.0 to get around many cloud disconnects. All are using I2C, not sure if that is related.
There is no way to use preview releases with with Web IDE.
You can however use the Particle: Cloud Flash from Workbench to upgrade devices remotely OTA.