Step 1
Download the kernel from below link

ftp://ftp.kernel.org/pub/linux/kernel/v

Step 2

Extracting  the kernel

if its a archive with tar.gz extension then do below in your /usr/src

# tar -zxvf linux-2.6.x.x.tar.gz

If its a .tar.bz2 then do below in your /usr/src

# tar -jxvf  linux-2.6.x.x.tar.bz2

Step 3

You must have a folder now in your /usr/src dir with the name of linux-2.6.x.x  just symlink it with dir linux

# ln -sf linux-2.6.x.x  linux

Now change the dir to linux

# cd linux

once you are inside the dir issue any of the below commands to configure your new kernel

# make menuconfig (This will show you a command line screen to configure the kernel)

or

# make xconfig  (This will open up a qt based gui window to configure the kernel)

Note : — if you want to configure the new kernel same as of  your old one then you just need to issue the below commands

# make oldconfig && make modules_install && make install

This will install your new kernel with the old config and also install the boot image and other files in your /boot

Step 4

I am assuming now that you have configured your new kernel and ready to compile it , just follow the below steps

# make && make modules_install && make install

Now just sit and have a cup of tea/coffee  as kernel compilation will take some time

Once the compilation is finished you need to reboot your machine and start using your new kernel

NOTE - i am assuming you are using grub here for that you need to select the option on boot for the new kernel

lilo users -  here comes  my lilo.conf

boot=”/dev/hda”
lba32
prompt
timeout=”50″
default=2.6.x.x
vga=”792″

image=”/boot/kernel-2.6.x”
label=”linux”
root=”/dev/hda4″
read-only
#       initrd=”/boot/kernel-2.6.17″
#root=/dev/ram0
#append=”init=/linuxrc real_root=/dev/hda4″

image=”/boot/kernel-2.6.20.3″
label=”2.6.20.3″
root=”/dev/hda4″
read-only