1. Open the Update Manager and click Check for updates/Refresh. After the check for updates in the Update Manager should appear one line with the proposal of updating mintupdate. Click Install updates. or
sudo apt-get update; sudo apt-get -y upgrade
Personally, I then rebooted the computer.
2. To upgrade to Linux Mint 17.3 Rosa in the menu of the Update Manager, click edit, where you should see the line - upgrade to Linux Mint 17.3 Rosa:
3. Click on this line to confirm, and then click Install updates and follow the on-screen instructions:
After the update is complete, restart the computer to start using Linux Mint 17.3 Rosa.
1. This upgrade method is applicable for editions of Linux Mint 17.3 Xfce and KDE, after they will be released as a stable release at the end of the current month.
2. Linux Mint 17.3 has a more recent kernel than that which is used in 17.2. This update does not change the kernel after the upgrade. But you can change the kernel, by installing the recommended kernel from the Update Manager - View - Linux kernels after upgrade to 17.3:
Do not forget to restart the computer