We should all be aware that when changing the service tier and/or performance level of a database it creates a replica of the original database at the new performance level and then switches connections over to the replica. No data is lost during this process but during the brief moment when we switch over to the replica, connections to the database are disabled, so some transactions in flight may be rolled back. So it probably best that you do this during a period of low activity.
It’s pretty easy to do, but heed Arun’s warning, as you can cause queries to fail during switch-over. My experience has been that scaling up is pretty slow, too: I seem to recall it taking 10-20 minutes for a moderately sized database.