dpi stands for dot per inch and it actually provides the size of the font in your system. If you are using a big screen and running Ubuntu on your computer, it becomes desirable that you increase the dpi of your resolution. Presently, I am working on a 22″ LCD screen and have increased the dpi of my system to make it easier for me to read.
The default dpi in Ubuntu is set-up to 96. To increase it, you will have to go to properties of the desktop. This you can do by right clicking your mouse or using the properties button of your keyboard. A window will appear and you will a “Font” tab on the upper side of this window. In this, the details of fonts and their appearance is provided. In this, this is a porting called “rendering” and you will need to click the “details” of this part.
Once you click the details, another window will pop-up and you can easily change the dpi of your system here. Usually, it can be done up to 106-110. Rest it depends upon you how much you want to change. Once done, you can close the window and return to your desktop and new dpi would have taken the effect.