You can easily upgrade over the network with the following procedure. Upgrades from Xubuntu 24.04 are supported. For all other Ubuntu systems, please read OracularUpgrades on ubuntu.com.
Run the update-manager application.
In Update Manager, click the Settings… button, and enter your password to start the Software Sources application.
Select the sub menu Updates from the Software Sources application.
Confirm the “Notify me of a new Ubuntu version:” option is set to “For any new version”, and change it if otherwise.
Close the Software Sources application and return to Update Manager.
In Update Manager, click the Check button to check for new updates.
If there are any updates to install, use the Install Updates button to install them.
Run update-manager -d.
A message will appear informing you of the availability of the new release.
Click Upgrade.
Follow the on-screen instructions.