Account
Your data is yours, with no lock-in. Back it up to a file, move it to a new phone, or delete your account for good, all from the Profile tab.
Go to Profile → Export Data. You'll get your full history as a single JSON file that you can save, send, or open anywhere. It's a plain, portable copy of everything you've logged.
Go to Profile → Import Data and choose a backup file. One important heads-up: importing replaces everything currently in the app with the contents of that file, so export your current data first if you want to keep it. After you pick a file and it finishes, tap Reload.
The easiest way is to sign in on the new phone with the same account, and your data syncs down on its own. The export and import route is there for when you don't use an account, or when you just want a manual backup file to hold onto.
Go to Profile → Account → Delete Account…. This permanently deletes your account and all synced data from the servers, and it can't be undone. It happens immediately, with no email required.