How to switch accounts?

You should be able to use multiple Garmin accounts. Each Garmin device is tied to a specific Garmin account based on the email address entered in the settings (Tools & Content).

My wife, my son, and I all share 1 computer with 1 Garmin Express. We all have our own Garmin devices that are registered to our own Garmin accounts. When we go to Garmin Connect we see only our own data.