how to set priority of os during boot
 

how can i set boot priority of the os through grub on ubuntu system on my laptop.

Depending of the version of UBUNTU you use you have a menu.lst or
Grub,cfg .
In both you find the line set default =
Default = 0 means the first Os in the list is the default .
Change the value in what ever you wise.
Use a real linux text editor to so
Do it as the root or sudo or su user.