If you are a user that has access to multiple tenancies, you may need to access data from different tenancies from time to time. To do this, you will need to switch between tenancies.
If you are not logging into a particular tenancy, once you log in, you will see a menu to select the right tenancy from. Simply click on it and you will be taken there.
From within a tenancy
The tenancies that you have access to is displayed in the left-hand navigation panel, with the current tenancy is displayed at the top.
To switch, simply click on the current tenancy (it will have a down-arrow to the right of the name) and select from the list by clicking on it.
Note that if you have the access to manage a tenancy, you will have an option "Manage Tenancy" displayed in the list also, above the other tenancies you have access to.