How can I remove / change the "Open With" list?

Enter the contextual menu of the file and go to the Properties of it. Then, go to Open with tab, right click on the application you want to remove and click on Forget association.

Goto ~/.local/share/applications, edit the file mimeapps.list:

In [Added Associations] section, you will find your file extension, something like this:

application/epub=FBReader.desktop;<another apps.desktop>

Which means there are two apps will be shown in "Open with..." menu when right click an epub file, identify the one for Dev-C++ IDE in your case and remove it.