How to change "Appointments" to "Lessons" in Buddypress?

Hello! I need to change just one word. I tried using the Ultimate Branding plugin to effect a text change, but it just created a recurring redirect. In the Buddypress profile menu, “Appointments” will appear so a user can change/edit their own appointments. I want to change this to “Lessons”. This is the only place that needs to be changed, since I’ve customized all emails and such. Is there a safe way to do this that won’t cause conflicts? I have a lot of plugins. Thanks!