In Syncee wizard's Field Mapping step you will find the Update options, where you can set everything you need when you would like to update your products.
You can find this setting here:
Would you like Syncee to rename the images?
If you select YES, Syncee will rename the images with a date and a code. Using this, Syncee will try to upload the images multiple times even if Shopify's server doesn't accept it for the first time. If you select NO, Syncee won't try to upload them more than once, but it is better for image SEO.
Sometimes Shopify's server does not accept the images that the application sends for upload. If this happens, Syncee will not be able to upload the image to your store. By deafult Syncee tries to upload images only once.
If you set this setting to YES, Syncee will rename the images with a date and a code and will use it to retry the upload of images if Shopify drops it for the first time.
If you set this setting to NO, Syncee won't be able to do this process, but the original image name is better for image SEO.
If you need further assistance, contact the support staff.