Do you mean switch to double ended needles? You can't knit in the round with regular straight needles because of the knob on the nonpointed end. If you do mean double points, just use one in the R hand and knit some of the stitches with it, then add another and another until all the stitches are on them. If you don't have dpns, then you can use another longer circular and do magic loop with it, or use 2 circulars and knit half the sts on each one. Just start knitting with the new needle.