Open the Start menu, and click on Programs -> Accessories -> System Tools -> System Information.
The System Information tool will display detailed information about your operating system. See the System Type. If it is x86-Based PC, then it is 32-bit and you will need to download Windows 8 developer preview 32-bit file.
After you have downloaded the required Windows 8 ISO file, it’s time to move on. The next step is to download Windows 7 USB/DVD tool. Download it here for free from the official Microsoft store.
You are now done with the downloading stuff. Install Windows 7 USB/DVD tool and run it. Step 1 is to browse and select the ISO file that you downloaded earlier. Once you have selected the file, click Next to proceed.
Select USB device and click Next to proceed.
Now plug in the USB into your computer and format it to have necessary space. If you already have data in your USB, make a backup of it somewhere. Once you are good to go, click Begin Copying.