First, I would say if you are changing frame size and combs then I would also change cell size to either natural comb or small cell at the same time. It will be the same amount of work. It just requires that you use either small cell foundation or foundationless frames.
The concept, of course, is to get to a point where all of the old combs (deeps, large cell etc.) are out and all of the ones you want (small cell and mediums) are what you now have. So first, you need to view all of what you don't want as a liability to be eliminated and all of what you do want as an asset. During a flow anything but brood is fair game to remove. During a dearth, honey and pollen are assets. At any time brood is an asset. At any time you can remove empty frames. There are several ways you can deal with any given deep frame. You can leave them in a deep and any excess that can't be filled with a deep (because you pulled them out) you can fill in with a medium. This is what I tend to do if there are more deeps than mediums. If you have more mediums than deeps, you can put the deeps in two medium boxes (it will hang down into the medium box below). If you have only one or two deeps with brood you can cut the comb to fit a medium frame and rubber band it into the medium frame. You can also get the queen and a couple of frames of brood on the other side of an excluder from the frames you wish to remove and wait for the brood to emerge in those frames and then remove them from the hive. These are the concepts.
So now to begin. The easiest time to begin is probably the first warm flying day in the spring. On a warm day you can look in the hive and pull any frame that is empty. You may have an entire box worth of empty deeps. Early in the spring there has been no flow to start refilling them and brood rearing is just getting into gear probably. The sooner you get the queen on the other side of an excluder from the combs you wish to remove, the better. If you have drawn medium frames, then try to get the queen on those. It's kind of early at lest in my part of the world to expect them to draw comb but they will be in about a month. So if you just keep removing empty frames until then, and after the flow gets into full swing you can steal any deeps with pollen and honey and harvest the honey. The pollen you can feed to the chickens (assuming there are any chickens) or cut them out and tie them into mediums (rubber bands probably...). Then applying the principles above you juggle things until all the boxes are full of frames. Later if you had comb on the bottom of a medium frame that was in a deep box, you can cut it off and rubber band it into a medium frame. If you have comb on the bottom of a deep (that was in two medium boxes) you can cut that off and rubber band it into a medium frame.
I don't know how to just make it a step by step unless I make assumptions about some brute force method, but that is also a possibility. You can simply do a "cut out" where you cut every frame of brood to fit a medium and rubber band all the combs into mediums and harvest all the honey and scrap or cutout all the pollen. If you have thin strips of brood left over you can put several in a frame to fill it out. This would be a "brute force" method and you could do it in an afternoon as long as there is a decent amount of nectar and pollen available.
A scaled back version of this is to cutout two combs of brood and put those with the queen on them on the other side of an excluder and wait for all the brood in the deeps to emerge and then pull them all.
If you don't want to do any cut outs of combs, then you could pull empty frames, replace with mediums and wait for the queen to be laying in some of the mediums and then pull those above an excluder.
All in all, I play it by ear and juggle it the best I can without stealing brood from them.