Imagine that there are few Windows operating systems on one PC, and there is a need to change the default OS for start up. Or maybe, one of the system was deleted from the PC, but it is still in the list of OS boot selector. Or user may want just to remove OS selection on boot. Thus user needs to change the boot items and change the default OS, or disable this option.

How to change start up order in the OS boot selector in Windows 7 (e.g. There were Windows XP Pro on the PC, but later user installed newer version of Microsoft OS, in this case Windows 7 and now user wants to make Windows 7 default OS):

1. Navigate to [Start] > [Control Panel\All Control Panel Items\System] and choose [Advanced System Settings]:

2. In the opened window of [System Properties], click on the Settings button:

3. A new windows with the system startup options appeares: 

 4. There is also ability to modify time of displaying the list of OS and turning this time off:

Note: be very carefull when changing OS boot order, if the fault OS is selected and time to display option is turned off, there can be difficulties with booting into working OS.