No. The new versions are completely separate programs that do not install directly over the older versions. You can have both versions running on your computer at the same time if necessary.
Installing the new version will not overwrite your existing databases. However, we have made so many changes to the database structure, it is not possible to translate your databases from a previous version to the new RainCAD version 7.5 or EcoCAD version 5.0. You will need to reenter the information in the new databases.
You can move any symbols you have created to the new program in a few simple steps. Refer to the Help screens or the Tutorial and Installation Guide under Customizing Existing Symbols for information on transferring symbol drawings.