It takes about a week or two after release before the upgrade path that is 'automated' with the upgrade manager or
do-release-upgrade is actually opened. (Why this is the case I'm not sure, but I think it has to do with bug squashing and bug handling of major issues detected post-release)
Patience is your best call here. It should be available within the next week or so.
If you are supremely impatient, and want to upgrade now however, you can try doing
sudo apt update && sudo apt dist-upgrade -y && sudo do-release-upgrade -d
... on the command line. However this could result in a broken system, or an unbootable system. So you do this at your own risk.
(The reason I don't recommend you upgrade yet until the upgrade path is open is because there may be major issues that are unfixed that will leave your system unbootable or usable post-upgrade. You upgrade now at your own risk.)