You can change your worker's name directly from your workers' list by clicking on the edit (pencil) icon.

If your worker is online and syncing with the minerstat dashboard, you can just rename it on the dashboard and your config.js on the rig will be automatically updated.
If your worker is offline and is not syncing with the minerstat dashboard, then you need to follow the next steps:
mstop to the console.mworker ACCESS_KEY WORKER_NAME to the console where ACCESS_KEY should be replaced with your access key and WORKER_NAME should be replaced with your new worker's name (e.g. W002).mstart to the console.ASIC Hub monitors groups and not worker's name, so all you need to do is rename your worker on the dashboard.