Allow switching to Ropsten by flipping a toggle switch in Profile > Advanced settings.
When switching networks, note that installed stickers will be uninstalled, and recent stickers will be removed. Sticker packs can be reinstalled after login. Purchased sticker packs will not need to be re-purchased, but will need to be re-installed.
Mailserver fleet information will **not** be updated. This can be controlled by a separate (undeveloped yet) setting.