I'd like to upgrade my existing gmail to a workspace account
There is no direct upgrade path for personal @gmail.com accounts to a Workspace account. What you will need to do is this:
- Purchase a Google Workspace plan of your choice
- Once set up, use Google's migration service (built into Workspace) to migrate (copy) your emails from your personal Gmail account to your new Workspace account.
It's possible to convert your existing gmail account into a Google Workspace account only if you no longer want/need to use your current gmail.com address.
If you do want/need to use your current gmail.com address, your options are:
1. Upgrade to Google Workspace individual (which uses gmail.com instead of your own domain).
2. Follow the path recommended by @cryptochrome: Create a Google Workspace account, the migrate your gmail.com account's email history, contacts, calendar, Drive files and other data.