When planning an image upgrade for a large number of Access Points (APs) across remote sites with limited WAN bandwidth, it’s crucial to minimize WAN utilization. The best approach in this scenario is:

Predownload the new code to the APs (Option A): This method involves sending the new firmware image to all APs before actually rebooting them with the new image. It allows APs to download firmware when network usage is low, thus minimizing impact during peak hours.

References := ( CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide )