Updating your pc
Well nothing is 'foolproof' really but here's the simplest method of making a FL Studio update or copying FL Studio between PCs and retaining all your files.
Updating an existing installation on a single PC - You may have saved data in the following locations, where 'OLD' is the version number of FL Studio you are updating from.
There is no risk that you will lose your FL11 data updating to FL12, so long as you don't delete the FL Studio 11 installation folder before recovering any personal data (see below).
It is possible to have parallel installations of various major and/or minor revisions of FL Studio.
It would be reasonable for you to install FL Studio onto each of these PC's, provided you are the only user of the program.
Registration also means you do not need to worry about losing your FL Studio Box code.
The FL Studio installer will copy the new installation files into the existing FL Studio folder (..:\Program Files (x86)\Image-Line\FL Studio 12), unless you set it to install elsewhere. Each major revision is installed into a unique folder ..:\Program Files (x86)\Image-Line\FL Studio 11 vs ..:\Program Files\Image-Line\FL Studio 12.