I have a lot of "type class" in the list, how do I remove those from the list I do not use?

The class names get listed when you use them. They will be different for each project. You cannot delete them from the list without also deleting them where they are used.

Then you can't erase those Type Classes no longer in use, taking unnecessary place on the Type Class list.

I'm assuming you are referring to the type class input box instead of elements of this type.
You can remove the class by hitting x in the type class input box. You can also click on the class and change it's name. I didn't see unused classes being retained in my test project.

First of all if a class name is given as a choice, then it is usually still in existence on one of your pages in your project.

There is a way but a bit messy, and to be honest not worth the effort, because when a project file id exported any unused class names etc, are not included in the CSS exported file anyway.

First of all save your project file with a different and meaningful name (IE: the date-time of the save. ) so you can make changes and if it gets messed up simple revert back to the previous saved project file.

When you select one of the CSS class names in from the drop down list, so for instance in your case let's say you select picture-13, it will add that class name to your image, and then tell you in the little section labelled "THE CURRENT SELECTOR" which other pages that CSS class name you chose, is located on. (you can also use drop-down in that to get a list of the pages where it is used If you select the other page(s) listed it will open that page, therefore allowing you to change that class name to something more meaningful or delete that class name if it is no longer required. HOWEVER this is where it could get messy, because if that class name picture-13 is the first or only class name, and you delete it then it will revert to an un-styled placeholder and you will have to re-syle it accordingly.

So in effect Inger and Eric are correct, in so much as a class name is automatically given a built in name (in this case picture-1, picture-2 etc etc, IF YOU don't give it your own class name before styling it etc etc, and you can change a default class name by deleting it and then immediately renaming it to a more meaningful name.

So in essence if Site Designer shows you class name that you think you don't use, then sorry but somewhere in your project IT IS STILL in use.

You can also check this by exporting your newly renamed project tile to a temporary file, then open the main CSS file with notepad or word or some other text editor an do a search for one of those class names that you think are not in use, id it finds it BOOM there you are it is still in use, if it doesn’t find it then that class name isn't used.