Almost all operating systems offer the possibility to customise the system start up process. Ubuntu has it's own "StartUp-Manager" but it is not installed by default. It can be used for managing the settings of your Ubuntu boot loader (Default operating system, time-out, etc.).
You can install it from the Ubuntu Software Center or from the Terminal by sudo apt-get install startupmanager
You can load it from System > Administration > StartUp-Manager sudo startupmanager
Very often users want to change the "Default operating system" (the operating system booted by default) or the Timeout (Time from showing the boot menu till booting the default operating system). Change the settings as wished and close (the changes will be automatically saved when closing).