Again, remember to keep the up and down strumming motion in your picking hand constant - even when you're not actually strumming the chord. Try saying out loud "down, down up, up down up" (or "1, 2 and, and 4 and") as you're playing the pattern. Listen to, and play along with, the strumming pattern, to understand how this new pattern should sound. Once you are comfortable with this, try it at a somewhat faster speed. If you're having trouble, put down the guitar, and practice saying or tapping out the rhythm, and make sure to repeat it multiple times. If you don't have the correct rhythm in your head, you'll never be able to play it on guitar.