You might want to stop the levo completely and ease into the Armour. The T4 in levo is going to stay with you for a while, but the T3 in Armour is going to affect you fairly immediately. So, for a while, your FT4 will be higher than it will end up. However, if you don't usually have any problems with meds, you could just make the switch and keep an eye open for any hyper symptoms and cut back for a few days if necessary.
How much are you switching from/to? Do you have current labs to post with reference ranges?