Microsoft’s free Windows 10 upgrade offer ends July 29, 2016. However, it seems there may be a way to receive your free upgrade but not have to commit to Windows 10 just yet. The article linked below is from How-To Geek and explains the process. We have not tried the process but in reading it through it appears to be possible. It also appears to require a fair amount of time and we certainly recommend backing up your system or better yet, imaging your system before proceeding (which they also recommend).
Keep in mind that after July 29, the Windows 10 upgrade is priced at $119, so you will have to decide if it is worth the risk of spending more time if something doesn’t go quite right versus just paying the $119 when you are ready.