help needed with template change please

I thought i had site builder plus ( I am on a mac ) but when i look to change the template i only see the 32 old ones ..i get the option to edit my site thru SBP but i thought the new templates would be there for me to see as well. Also can I play with the templates and if I dont save do I still have my old site or do I have to give that up to have a go and see if a template would look better ? thanks