I ever encountered a serious damage after i tried to upgrade my kernels when I was newbie.Now,I sum up the method for upgrading Linux kernel to 3 steps for you.I hope it can help.
Step 1,Of course ,first of all,you need to download the updatest kernel packge from www.kernel.org.
Step2,Open you terminal and then run:
#cp linux2.6.24.tar.gz /usr/src
#gunzip -d linux-2.6.24.tar.gz
# tar xvf linux-2.6.24.tar
//Uncompress the package and then load to the filefolder(I use 2.6.24 kernel as sample)
Steps 3,installing the kernel:
#make mrproper //clean system
#make menuconfig //configure menu
#make xconfig //configure kernel and delete drivers and language files which is not relevant to your computer.
#make //complie the kernel,normally it takes half hours or above,depending on your PC speed.
#make install //install!
#reboot Now,you will see your booting menu has been added a new column that is your installed new kernel.