Short answer
HubSpot's KB: Super Admins choose Actions > Uninstall Salesforce, then remove the HubSpot integration package in Salesforce. HubSpot doesn't recommend uninstalling and reinstalling to fix sync errors.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Work through sync errors before considering this.
3. Related
Integration settings and sync errors.