Unable to update the Approval process set up for journal approval

Hi,

We are having some issue while updating the approval process set up for journal while trying update the user list. We have created a new Journal approval process and assigned a user list. The process works fine. Now we need to make some changes on the path, step and user list of approval. Now the option to edit user list and '+' button is no longer available. I have seen some comment somewhere that it is becuase there are some transaction sitting already in the system which uses this approval process. In this case, is there a way to update