Slices for Web

First time creating slices in AI for an email to export for web. I want to edit my bounding box for slices and it is very frustrating, it not working seamlessly. It automatically creates another slice and then I cannot edit that bounding box. It is so glitchy too, will not adjust the box to the graphic. I just received a notification for increase in monthly subscription and for what, I cannot do a simple email slice. Ughhh