This feature is available for Admins, Teachers, Assistants and Students. To update the language you would simply click the gear icon next to your name. For Teachers and Students this is in the top right hand corner and for Admins it is in the lower left corner.
From here click on Language and in the pop up simply select the language you want to use. Since it is English by default, you would click the dropdown arrow next to the word English and choose Spanish.