You can edit your workout logs in the app and on the website. Editing a log in any location will change it everywhere. You cannot restore an edited log back to how it was originally, but you can edit logs as many times as you like.
Log into your account and find the log you want to edit. Click the "pencil" icon, then enter a new distance and/or time. When you're done, click the green checkmark icon.
iPhone and Android
Open your "Workout Logs", then tap the run you want to edit. Tap the 'pencil' icon next to the mission title at the top of the screen, and now you can edit your distance, time, calories, or steps. When you're done, tap the back arrow at the top left.