The Final release of Ubuntu 15.10 Wily Werewolf will be out in a few days on October 22. Below is how to upgrade your existing Ubuntu 15.04 to Ubuntu 15.10.

Preparation

1. Backup Data. You should back up your important documents, files, bookmarks, etc.

2. Disable PPAs. Some PPAs may cause the upgrade fail, so do disable all third-party PPAs in Software & Updates -> Other Software tab.

3. Uninstall video driver. If you’ve manually installed proprietary drivers directly from the manufacturer’s website, then before upgrading I recommend you removing these drivers first and reverting to the open-source drivers.

Upgrade Ubuntu Desktop:

1. Open terminal from the Unity Dash, App Launcher, or via Ctrl+Alt+T shortcut key. When it opens, run command to update your system:

sudo apt-get update; sudo apt-get dist-upgrade

2. After that, launch Software Updater via below command:

sudo update-manager -d

Below window should pop-up and prompt that Ubuntu 15.10 is available for upgrade:

Click the Upgrade button and confirm again in next window. Software Updater will fetch and install the files and prompt you to remove unnecessary applications.

Restart your computer once the upgrade process finished.

Upgrade Ubuntu Server:

1. Backup your configuration files if you’re running any services on Ubuntu server.

2. install the update-manager-core via command:

sudo apt-get install update-manager-core

3. Edit the config file via below command to make sure there a line says “Prompt=normal” (without quotes):

sudo nano /etc/update-manager/release-upgrades

After editing, press Ctrl+X -> type y -> finally hit Enter to apply changes.

4. Finally upgrade Ubuntu Server via command:

sudo do-release-upgrade -d

Follow the on-screen prompts and done!.

Sumber: https://ubuntuhandbook.org/index.php/2015/10/upgrade-ubuntu-15-04-to-ubuntu-15-10/