Please note that this is ONLY TO RESERVE THE FREE UPGRADE, made available July 29th; this is basically telling Microsoft that you want it. ITâ€™s NOT GOING TO INSTALL IT IMMEDIATELY! If you want to use Win 10 now, go to insider.windows.com and download the ISO.
Thatâ€™s it. Hereâ€™s the link to the FAQ thatâ€™s in that dialog.