Windows 10 problems

I have an Inspiron 1545. I recently upgraded from Windows 7 to Windows 10. Whenever I start the computer, the icon in the bottom left of the screen doesn't work. I can get it to work by removing the battery, removing the power lead, powering off and re-starting. I now learn that Windows 10 is not designed for my old laptop, so my question is: - how do I uninstall Windows 10 and re-install Windows 7.