Hi, I just had the same question and I ended up figuring it out.
1 - Open Safari browser.
2 - On the upper left corner, there are three color circles, one red, one yellow and one green. Right next to the green one, there are the two "arrows" to navigate back and forward to the pages you have recently viewed. Next to the "arrows", on their right side, there is another icon, a rectangle divided vertically. This rectangle is the "sidebar" icon.
3 - Click on the sidebar icon. It will open the sidebar on your browser and there are three options on top: the first one is for "Favorites" , the second one is for "Bookmarks", the third one is for "Shared links".
4 - Click on the "favorites" icon: it will turn blue.
5 - Select the webpage you want to delete from the "Favorites" by pressing the "command" key on your keyboard and mouse-clicking (or trackpad-clicking) on the item of the "Favorites". Release both the command key and mouse (or trackpad).
6 - Press the "delete" key that has a little black arrow right to it. This should delete the item from "Favorites".
Please, let me know whether or not it has worked for you.
Sincerely,
Alex.