1) Click on 'Settings'
2) Click on 'Configuration'
3) Click on 'Bookings' (second from the left)
4) Click on 'Edit'
5) Click on 'Add an item'
or, click on the trash bin icon if you want to delete an item.
*note you can also tick or untick the 'require for all bookings' checkbox for each of these options.*
6) Type in the new item name
7) Click on 'Save'
8) Click on 'Accommodation' to go back to the accommodation/booking window