How do I add my landlord onto my business insurance policy?

I just moved into a new business location. My lease states that I must list my landlord as an additional insured. Is that easy to do? Do I just call my insurance and have them add right away or do I have to wait until it is time to renew? Also, approximately by what percentage will that cause my insurance to go up? I have already had a rate increase because I live in Louisiana (Katrina). It is still affordable but I am scared that adding on the additional insured may cause it to double, which I can't really afford.