What are the steps to remove a plugin?

@seani : As of my knowledge No need to close application server or appian for deleting .jar file from plugins folder but close process model canvas, you can find log file message like this.
Smart service plug-in [plug-in name] version[plug-in version] uninstalled successfully.

IMPORTANT:

DO NOT DELETE THE CDTs related to a plug-in as suggested by one of the users in this thread. This is not a recommended practice because if you then decide to re-deploy the plug-in you'll then face this issue: forum.appian.com/.../kb-1097.html

@Eduardo: Sry if I was misguiding. I was suggesting based on my experience in working on plugins in 7.2. Normally when we un-deploy a plugin to modify the structure of a CDT within the plugin and try to deploy it again, it wont override the CDTs in Appian similar to calling a web service with modified CDTs. We used to search the CDT in Appian, delete it and deploy the plugin with updated CDT successfully. The pain point sometimes is to search (after deleting the old plugin version long time before) through 100s of CDTs and find all the CDTs associated with the plugin and delete them. And this is not keeping in mind of any existing instances still using the old CDT. Its all about modifying a plugin which is not fully implemented in an application. Hence I mentioned unused CDTs.

When its a plugin used by a process which has running instances, Yes we have to follow the best practice as you have pointed out.

Thanks for the link you provided.

That's correct, if the change to the CDT is intentional, you do need to delete it and at that point you need to make the changes suggested in that link to create a new smart service with the new key to support the change in the input/output type.

I wouldn't recommend to delete the CDTs if it's not in the plan to update the CDT. Thus my comment before to clarify.