You can do it one of two ways:
1) In the spring shake them down on to small cell foundation
2) Just start feeding in frames with small cell foundation or with starter strips
The first one is a little faster, the second one a little slower, but less disruptive to you and them. I am regressing two hives using the second method, I'm in my second year of regression and for the most part they are drawing out the small cell foundation beautifully now. The first year of regression resulted in alot of reworked comb and eventually by end of summer, some correctly drawn 4.9 cell comb. It takes some time, but everything seems to be working fine.