You need to stop and remove the old container first, then pull the latest image and run.
Or let Watchtower update it.
Here's how I update my Portainer (of course you need to use your version of the run statement)
docker stop portainer
docker rm portainer
docker pull portainer/portainer-ce:latest
docker run --detach --env 'TZ=America/Los_Angeles' --name=portainer --restart=always -p 8000:8000 -p 9000:9000 -p 9443:9443 -v /var/run/docker.sock:/var/run/docker.sock -v /volume1/docker/portainer:/data portainer/portainer-ce:latest