By whatever means appropriate for the boot loader you've chosen to use.
With Linux, there are several possibilities; Grub and LILO being the
most common choices. Find out which boot loader you use, then read
the corresponding doentation.
Wolf a.k.a. Juha Laiho Espoo, Finland
(GC 3.0) GIT d- s+: a C++ ULSH++++$ P++ L+++ E- W+$ N++ !K w !O !M V
PS(+) PE Y+ PGP(+) t- 5 !X R !tv b+ !DI D G e+ h---- r+++ y++++
"...cancel my subscription to the resurrection!" (Jim Morrison)