How to switch from a 32-bit operating system to a 64-bit one?

Hello

First, save all your personal data outside of the PC.

Download the 64-bit version of your OS, for example, there are plenty of free OS options on Distrowatch
http://distrowatch.com/

For instance, Mint is currently the most installed
http://distrowatch.com/table.php?distribution=mint

Look for French-speaking websites
http://www.linuxmint-fr.org/
http://www.linuxpedia.fr/doku.php/debuter

or installation tutorials in French (this one is not recent but remarkably clear)
http://www.linuxmint.com/documentation/user-guide/french_kde_9.0.pdf

Another distribution that allows you to change the desktop environment without restarting
http://distrowatch.com/table.php?distribution=hybryde

If you have a little money, you can buy a 64-bit Windows
(there is a compatibility test for your computer to install the 64-bit version and tutorials in French)
http://windows.microsoft.com/fr-FR/windows7/products/features/64-bit-support

In some cases, if you don't have a CD drive, you can create a USB installation stick:
http://www.commentcamarche.net/faq/21013-windows-creer-une-cle-usb-d-installation