It is mentioned on the IRCC website. You can't change DLIs if you have not first "actively studied" (one semester) at the original DLI on your study permit. You need a new study permit if you have no plans to study at the school you received your study permit for. IRCC changed the rules a few years ago to stop students from entering Canada and changing DLIs.
If your application has been approved
If your application for a study permit has been approved and you change your DLI, you must submit a new study permit application with a new letter of acceptance. You must also pay all the fees for the new application.
Too many people were doing this which is why you now need to reapply for a new study permit unless you were actively studying your first program before changing to another degree.