Thank you very much.

"...install a 64 bits version of Java on your system, download the Jar executable version of Sweet Home 3D and execute the java -Xmx4096m -jar path\to\SweetHome3D-3.7.jar command for 4 GB... "

The first two steps are OK, the execution of the command should be done in the windows command line? (I did it, but not sure if something happend)