You can upgrade your linux system using the package manager APT which is available on debian based distributions:

First we have to update all the packages installed:
$ sudo apt-get update
$ sudo apt-get upgrade
Now we make sure that we have the update-manager-core package installed with:
sudo apt-get install update-manager-core
Then we start the upgrade
sudo do-release-upgrade

This tutorial assumes that you are a sudoer running Gnome
What is .chm
Wikipedia says:
Microsoft Compiled HTML Help is a proprietary format for online help files, developed by Microsoft and first released in 1997 as a successor to the Microsoft WinHelp format. It was first introduced with the release of Windows 98, and is still supported and [...]