Before installing a newer version of Serato DJ, find the existing Serato DJ program folder on your computer and rename it. It's very important to rename the FOLDER, not the .exe. Renaming it after the version number is a useful way of identifying each version - especially if you plan on installing multiple versions. For example; if you currently have 1.5.2 installed, rename the folder Serato DJ 1.5.2.
(The Serato DJ program folder is located by default in C:\Program files (x86)\Serato)
Now, when you install the new version, the old folder will not be deleted, and you can choose which you want to run by going into that folder and double clicking on the executable. You could also create shortcuts on your desktop for each version if you wanted to.
(Right click on each .exe, choose Send To > (Desktop create shortcut))
You will need to uninstall your current version if you wish to revert to an older version of Serato DJ, however you can still use the method above to install multiple, newer versions of Serato DJ - than the one currently installed
Before installing a newer version of Serato DJ, go to your applications folder, and rename the existing Serato DJ application file. For example; if you currently have 1.5.2 installed, rename Serato DJ to Serato DJ 1.5.2
Now, when you install the new version, the old application will not be deleted. You can choose which you want to run by clicking on the applicable version in the applications folder. You can drag any number of these applications to your dock for quick launching. (The dock will not automatically update with a new installation)
Warning: It is not advisable to run more than one instance of Serato DJ at one time. Doing so could cause problems with your Serato DJ database.