Does windows 7 stay on the computer or get deleted? if it does delete windows i wont download Ubuntu. So, does windows get deleted? and if not how to i change back and forth between the two?
You have the option to Dual Boot between Windows 7 and Ubuntu. Typically this works well and you will be presented with an option to boot Ubuntu or Windows every time you boot. The important thing to watch for if you want to keep Windows is when installing, choosing the option to install Ubuntu side-by-side. Here is more information on Dual Booting Windows and Ubuntu: https://help.ubuntu.com/community/WindowsDualBoot
Does windows 7 stay on the computer or get deleted?
You decide when installing Ubuntu. You can keep Windows 7 and boot into both; or you can remove Windows 7 completely.
and if not how to i change back and forth between the two?
If your computer came with Windows 7 then probably by using Grub 2. It shows a menu every time you start the computer that lets you choose which OS to boot. By default it will auto-boot Ubuntu if you don't change the option within a few seconds. This is automatically set up if you install Ubuntu on a drive that already has Windows on it.