When you upgrade a version of VideoStudio - even with the reduced price 'upgrade' version it does not change or affect any previous version. So after you install the new X5 version you will still also have a full and working copy of X4 on your computer complete with all your projects - the two programmes will both still be fully working - though you will not be able to use them both at the exact same time. Your projects will not automatically transfer to X5 but you will be able to open and edit all your X4 projects in X5 by simply browsing to them and opening them - but a straight reverse is not true - you cannot save a project in X5 and open it in X4 UNLESS you specifically "Save As an X4 version" in X5. Similarly if you have special libraries set up in X4 you will need to manually export the library to your hard drive (using the built in Library manager) and then manually import them to X5 - again using the included Library manager.
Please note that the 'X' in the version number is important as it is the Roman numeral 10 and defines the difference between current versions 18 & 19 and the very old 8 & 9
My VideoStudio demo videos - https://www.youtube.com/user/MrBrianCee