How do i Grow out Frankie Sandford style hair.?

I've had Frankie Sandford style Asymmetric hair cut for a while now and i want to grow it out. the longer side is past the bottom bit of my jaw and i want to keep that bit long whilst growing it out. my Hairdresser says to cut the long side short but i don't want to. how do i grow it out?!?!?!/