CWWBF0024E Process [YOUR_PROCESS] of application [YOUR_APP] is not stopped. Stop the templates manually before updating or uninstalling a process application

You have to stop the process template first, before any updates to the process can happen. It wont help to restart the application or even the server.

Go to websphere process server admin console /ibm/console.

Go to ‘Applications’ -> Enterprise Applications > YOUR_APP > EJB Modules > YOUR_APPEJB.jar

Go to Business Processes and stop the running process template. Save changes. There is no need to restart the server.