How to remove deregistered/inactive task definitions

I want to ask you, how to remove inactive tasks definitions from ECS. I removed everything from ECS, clusters, cloudformation, services, etc. but tasks still stay on my list. For example when I create new one with the same name like the one form old then the old one change status and get a new revision. But I want to get a new one without old revision. I have a lot of inactive task which I will not never use. How to remove it?