I want to show all content type fields when editing a list in Sharepoint 2013.
At the moment I am getting a drop down window and I have to choose between content types.
Is there any way to show them all on the same page ?
No you cannot show fields from different content types while editing an
Item and this is the SharePoint's OOB functionality.
Item in SharePoint is associated to only one
Content Type. So while editing an Item it is theoretically incorrect to expect fields from the other content type, to be displayed on the Form.
Also I will never recommend to go ahead and customize your
Edit Form to show fields from other content types.