Windows 10 is being released on Wednesday, July 29. A free upgrade (for one year) will be offered to current Windows 7 and 8.1 users. Your computer should already be configured to get this upgrade.
Microsoft is going to be "nagging" existing Windows 7 and 8.1 users to take the upgrade after July 29 -- not everyone is going to be offered the upgrade at once, it will be offered in waves. If you are an existing user, you probably already have a white Windows icon on your tastkbar confirming that your reservation for Windows 10 is already set -- it is on the far left here:
You can find out more about the process for getting a free upgrade here.
Should you accept the free upgrade immediately?
Some publications are recommending that you hold off on accepting the Windows 10 upgrade at first, particularly if you use Windows 7. Check out this Computerworld article on why you might want to hold off:
Other publications are raving about Windows 10 -- calling it the best Microsoft release in quite some time.
My own advice is this -- if you like new technology, and like to experiment with new things take it. Windows 10 is a natural development for Windows 8.1 users who will be immediately used to the new interface.
On the other hand, particularly if you are used to the simplicity of Windows 7, you might want to hold off for now.
I am undecided on what I am going to do -- I am a Windows 7 user. I will let you know my decision on upgrading when the time comes.