Question: Recently I downloaded ubuntu 13.04 (iso). Now after extracting the iso file and running wubi - it says downloading required files though I had already downloaded the iso file (794 MB). So what to do now?

Answer: 
Use the ISO that you have downloaded. You can make a boot-able pendrive by using this utility at <http://www.pendrivelinux.com/>. Then you can install ubuntu using this pendrive. 

PS. : in your boot options just check that USB is higher priority to the hard-drive.

Also, Wubi currently is not the best way of installing Ubuntu. You can read it for yourself [here](http://www.omgubuntu.co.uk/2013/04/wubi-advice)
DO NOT extract ISO files. Instead mount it using ISO mounting program, and run Wubi. I suggest use Wubi only when you using Ubuntu [12.10](/questions/tagged/12.10 "show questions tagged '12.10'")

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If you mean installing it on its own partition, instead use [live-usb](/questions/tagged/live-usb "show questions tagged 'live-usb'") from [pendrive](/questions/tagged/pendrive "show questions tagged 'pendrive'") using [UUI (Universal USB Installer)](http://www.pendrivelinux.com/).