Do I have to install all the old versions before installing the latest?

No, you only need to install the latest version. Each update install will overwrite the previous version.

If you want to keep an older version of the software (Serato DJ for example) while installing a newer version, make sure you rename the old application file something different.

For example, if you are using Serato DJ 1.6, and you want to install Serato DJ 1.6.3, rename the old application file "Serato DJ 1.6", then when you install the newer version the software will not overwrite that application (it will just be called "Serato DJ").