Windows 7 is a lot more powerful and stable than its predecessor, Windows Vista. The easiest way to get Windows 7 up and running on your computer is to find a Windows 7 download and install/upgrade your computer from there. You can be running Windows 7 within hours from now.
Here I will explain exactly what you need to do.
Before you can start you need to determine which version of windows 7 you require… There are 3 main versions of Windows 7 – Home, Professional and Ultimate, and most users will find the home version adequate. The professional version includes more networking options and is recommended for business use. For corporate networks and systems, the Ultimate version is ideal.
Also check the system requirements for each version of Windows before you buy to make sure you will be capable of running Windows.
Now to get started

Then you need to download a Windows 7 iso image file.
To do this, go to Microsoft's website and purchase the required version of Windows. You simply need to select Download only and after your purchase you will get your windows 7 download link to the ISO image file.
Also take note of any emails/confirmation screens you receive to keep a copy of your serial number and activation keys.

Burn the downloaded image file to a DVD. You can use a free program such as IsoBurn to perform this step. Simply open IsoBurn, choose the downloaded Windows 7 iso, and select your DVD drive. After a couple of minutes you will have a full working copy of Windows 7, ready to install.

Backup all your important files and documents to CD's/DVD's/Flash disk and/or hard drives. Usually upgrade perform without any troubles, but rather be safe than sorry. Once you are ready to install, simply insert the DVD into the drive and follow the prompts from there.