Browse to the navigation on the left hand side of your Pinpoint Admin Screen and select 'Interview Types' under the 'Settings' section:
Locate the Interview Type you wish to edit and then click the edit button to the right of it:
Make any changes you wish and then click 'Update Interview type':
Note that this will change any pre-existing interview stages that use this interview type. Whilst this isn't a major issue, it would mean that when you look back at an interview historically, you may think that it was for example a face to face interview when in fact it was phone based.