Just take it out of the party cup ,carefully and put it into its final pot.I have been growing auto's for ten years .I transplant twice from party cup ,to medium container, to final container.I have never seen any difference in a plants yield due to proper transplanting. I have done both ways. Infact my last run of sweet seed s.a.d. the 2 plant i transplanted several times( due to not having room in the grow room for larger containers at the time) ended up being the biggest and best yielding plants.