dual boot win 8 and 7

Hi,

I got a now Envy 15 and I'd like to have win 7 for operating some old fashion softwares. I have win 7 and its key and I made its bootable image. I mounted image on a thumbdrive by microsoft appropriate software. Now what can i do? In old fashion computer i had to change bios boot priority, how about here? I don't know anything about new bios and uefi.

Thanks,