Hello, welcome to LQ!
Do you mean that you want to install a new version? If that is the case, you can just install over your current installation using the tools in the installer. For instance, when you are asked which partition to install the / system to, you can just assign it to where your current installation is. BUT BE CAREFUL! If you are dual booting with windows, Ubuntu will use your entire hard drive if you let it. Make sure you use manual partitioning and leave your windows partition alone. There are a lot of patitioning schemes you can use (using /home on a different partition, for example.) You might want to check the Ubuntu forums as this is covered quite extensively there. Just go to the Installations and Upgrades section of the forum and use the search function.