whats the next step for training my budgerigar

He's about 15 weeks old. When i put my hand in the cage with some spinach in it he jump straight on to it and happily eats away. Is he's next lesson for him to get on (in the cage) without the treat or should i try and get him to come out from the cage on my hand while still eating??

You've got it right!

When he jumps onto your hand for the spinach, give him the cue, "Step up". or "Up,Up", whatever you want the cue to be for stepping up on your hand. He will then begin to associate the cue with the action of the stepping up and the reinforcer.the spinach.

When you are first training anything, you want a one-to-one ratio schedule of reinforcement. That is: one cue and one execution and completion of the behavior asked equals one treat.

Your next step should probably be to get him to come to the door of the cage with the door open and have him step up to you outside the cage. When he does, treat him and praise wildly! Good Boy! Immediately have him step back into the cage on the perch. Praise and treat him for that too! You want him to be able to step up and step off your hand with equal skill. So he needs a treat for that too doesn't he? He's also learning that he gets to go back to his safety zone with no trouble.

Do that several times until both of you are comfortable with it. Then, when he steps up and is eating a treat, back away from the cage a step. Keep treating. Praise wildly! Then put him back and treat again. Praise wildly!