We are aware the current version iOS app crashes when opening Account Options. A fix (2.1.7) has already been submitted to App Store for review, it should become available in approximately 3 days.Meanwhile, please use the Web interface to change login email and password, and other account options such as adding tag managers and limited user accounts, which are not supported using the iOS app anyway. UPDATES: This has been fixed in 2.1.7 that was released today (May 23).
Also we are aware if you live outside of USA/Canada, the new native iOS app temperature graph had been crashing for 2.0.x and 2.1.x. This has just been fixed from the server side, no app update is necessary. It was due to the server auto-adjusting date format to native format used in your culture/country, and this confused date parsing code in the iOS app code. You will still get localized date format if you access the temperature graph from Web, only when the data is access by the graph code in the app that the server stops to localize the date format.