Hi Arnaud,
Thanks for using Syncfusion products.
All our latest Essential Studio setup (12.1.0.43) versions are compatible with .Net framework 4.0. Please refer the below mentioned help link for more information.
http://help.syncfusion.com/ug/common/documents/minimumsoftwarerequi.htm
Please refer the below help link for upgrade to new Syncfusion version.
http://help.syncfusion.com/ug/common/documents/howtoupgradetheproje.htm
Please let us know, if you have any queries.
Regards,
Sivaguru S