Assuming your referring to the Anaplan Way Application. You should be able to remove, add and edit a project in the administrative dashboard. Would not recommend deleting the project directly from the list though. You might create orphans in other modules. I'm not sure about the referential integrity in that application.
If you're trying to remove a model from the workspace, you can use "manage models" for that. I would not recommend deleting though, rather archive the model. There's not space penalty for archiving.