factory reset MacBook pro OS Sierra 10.12.3
I just purchased a MacBook Pro running macOS Sierra 10.12.3, in the apple store I set up my new mac using a time machine back up of my old MacBook. Now I regret this as I have brought over a lot of junk files and programmes. I would like to factory reset the new MacBook to start fresh with only the files and programmes I want. All my data is still stored on the old MacBook and on an external hard drive. How do I factory reset the new MacBook?
Thanks
MacBook Pro, macOS Sierra (10.12.3)