Should we rename the default Administrator account in Windows?

Renaming it alone doesn't solve the bigger problem. The built-in account has a recognizable security identifier even after a rename, and a shared login makes it hard to tell who did what.

Move people to individual accounts and give them only the access they need. Use separate administrative accounts where elevated access is required, rather than having everyone use the built-in account for daily work.

Before disabling anything, check what depends on the account. Scheduled tasks, services, scripts, backups and integrations are worth looking at. Replace those uses with suitable service accounts and test them.

Make sure you have another working administrative path, then communicate a cutoff date and disable the old account in a planned window. Test after a reboot too, since some dependencies may only show up at startup. Keep a recovery plan in case something was missed.

For workstation maintenance, look into Windows LAPS. It can manage and rotate local administrator passwords so you're not relying on the same shared password everywhere. Check the deployment and directory requirements for your environment before choosing how to roll it out.

Don't overlook the people side. Find out why the account became the main login and agree on a transition plan with whoever owns the affected systems. A cutoff date and clear access changes will go much better than quietly turning it off and waiting for complaints.