You will need the Full Write Workflows permission, be an admin on the associated workflow, or a manager on the process to perform this action
There are multiple ways to do this.
From Person's Profile
Navigate to the person's profile and click on the "Involvement" tab and then on the "Queues" sub tab. A list of all the processes they are in will appear.
From Queue Listing
Click on "Automation > Queues" from the left hand navigation. A table will appear showing you each person and the workflow process task they are currently in (could be multiple rows for the same person).
Next, click on "Delete" from the drop down menu at the end of the appropriate row you want to delete.
From Process
Navigate to the process which contains the person you want to remove and click on the "Queue" tab. The list of people currently in the process will appear. Click on "Delete" from the drop down menu at the end of the row containing the person you want to remove.
A confirmation message will appear. Click on "Yes" to finish removing them from the process.
Helpful Tip
Removing the person from the process will not delete them from the system. The person's profile will remain.