i don`t known how to delete windows xp from my computer?i had just format my computer the day before yesterday and it shows the two windows option whenever start.

I think you need to use BIOS
or you can just BIOS auto boot to a diffrent drive(There by using the OS on that drive)

When you installed the new OS, you needed to have deleted existing partitions. This option is a available in the early stages of the installation.

Otherwise, if you install to an additional partition, the result will be a multi-boot capable system.