To update your system version you should fully update and upgrade your current version of Ubuntu with “apt”:
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sudo apt uptade
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sudo apt upgrade
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sudo apt dist-upgrade
you need also to remove all unnecessary packages:>
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sudo apt autoremove
now let’s start update the system. It is easy you just need execute some simple commands the rest will do instead of you the system. First you need to install the next package. Run this command:
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sudo apt install update-manager-core
Now you can run the Ubuntu upgrade utility:
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sudo do-release-upgrade
But if after execute this command you get some massage like this “No new release found” add the flag “-d” at end of command:
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sudo do-release-upgrade –d
when you add that flag you force the system to upgrade. After that the system will ask you several questions about how you want to handle the upgrade and it will start upgrade.