[Trisquel-users] How to edit bootloader in Trisquel GNU/Linux 6.0

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I am using Trisquel GNU/Linux 6.0 and I want to edit my bootloader to add  
another OS(Fedora,which was not detected automatically on installation.only  
windows xp  was detected). Also i want to change the background image of grub  
bootloader.How can i do this.