Heh...very slowly. Usually, what I do, is to mix up a couple of gallons of water. I use one gallon containers, so I fill up the container most of the way, and then I use the remainder of the water to acclimate the betta. I add about 1/4 of the amount of water the betta is already in every 1/2 hour until their container/bag is full. I then net them out of the water they were in and put them into their new home. It's a slow process, but it works. Even the two bettas that came from Thailand acclimated well with this method. I think there are other things you can do, but this is what I do. Oh, and I usually add some stress coat in the water on the first transfer.