The Windows Update should be able to find already downloaded files automatically. If you wait a few minutes, did it find the files? If it doesn't work, an alternative is to use the Windows Download Tool.
Of course, using the Windows Download Tool will require you to keep your computer on. However, this is an alternative to using Windows Update if Windows Update turns out to be unreliable even if you do keep your computer turned on.
Download the tool (either 32 or 64 bit), run it, and select "Upgrade this PC Now". The tool will download the files and install Windows 10.
For Activation, it should happen automatically upon installation and reboot.
If Windows Update does not resume by itself, and you really need the ability to resume upon reboot, the next option is to use GWX (Get Windows 10). The GWX app uses peer-to-peer method of downloading Windows 10 files. The problem is that you won't get to control when it downloads, as it all depends on the available peers. You should already have the GWX app from KB3035583.
I want a solution which will resume its downloading, does tool support resuming ? – d.Siva – 2015-08-25T04:45:51.533
Unfortunately, the tool does not support resuming. If resuming is not working for you in Windows Update, the next best option that also has "resume" is the GWX (Get Windows 10) app. GWX uses a peer-to-peer protocol to transmit files. You don't really have much control over it like when it downloads, though. I've updated the original answer with this information and some details. – nehcsivart – 2015-08-25T04:47:55.670
Much Thanks, I will try doing this and if it works(which i think will) i'll accept answer. – d.Siva – 2015-08-25T04:57:56.257