Pleased to tell you that Windows 7 is supported on that Dell model, but only 64-bit Windows 7, so make sure that's what you install.
When you've got a Windows 7 64-bit DVD, make sure the hard drive you want to install Windows 7 on
is the only hard drive connected to the system.
Boot your PC from the DVD and Windows Setup will appear.
You can delete the existing Windows 8 partition and create a new partition by following the prompts and pressing the appropriate keys as shown on screen.
You then choose that new partition to install Windows 7 on.
At some point you will be asked to enter the Product Key which you'll find printed on a card included with the DVD.
When Windows is up and running you should find that the ethernet port can be used to access the internet using the default Windows network driver, if not use a different PC to download the drivers from Dell's website and copy them to a pen drive or a writeable CD then transfer that pen drive/CD to the Dell Studio to install the drivers.
For US Dell models go here and enter serial number of the PC or use "Auto detect product":
http://www.dell.com/support/home/us/en/19/Products/?app=drivers
For UK Dell models go here instead: http://www.dell.com/support/home/uk/en/ukdhs1/Products/
For other countries click the link at bottom right of either Dell page.