Hi Rafa?,
Thanks for opening this thread.
WordPress handles the limits for uploads and not Advanced Ads. So you can decrease the maximal file size globally, but this limit would affect all actions, including uploading images for your content. Here, you can find a post that describes several options to set these limits.
Suppose you want to avoid that the ad managers on your website can upload images with heavy file sizes, but in addition, you don’t want to limit the file sizes of your content images. For this purpose, please check this section of the post, in which the author shows an example of how to limit the file sizes for specific user roles.
I hope that you can resolve your issue with this idea.
Best regards,
Joachim