The update size is around 750-800MB, but we strongly recommend you to have at least 1GB of free storage space since the files are extracted which can increase the size. Low storage space: You need at least 1GB of free space to download the update.Depending on your region and carrier, it may take a few days for the update to be rolled out for your device. Region & Carrier: The update roll out process is affected by your cell phone carrier and region.Possible Reasons for Update not Downloading If you have it installed, you are already running the anniversary update. Anniversary Update for W10M is build 14393.67.