Put them near the top with gooe current (not enough to blow them away but enough that they are getting some). They will spread fast (that is the fun part). Leave the actinics on for 12 hours and the pc on for 10. If ou are running less than this now, sloooooly make the move toward the desired photoperiod. everything will be fine as you make the adjustments, and nothing will bleach from light shock. If you are running more the change can be quicker, but still do it over a few days at least.
Luke