hi
if u r used text mode then use the command "redhat-confg-Xconfig"
then select the type of minitor that suits for u.
then for updating the package or for installing the package that u have not selected while installation for that :
**if u r having X window(gui mode) than select add/remove application in the start menu (it might be sub menu of one of the "system tools" or "system settings".
select it and then in next window select the packages u want to select and insert the cd 1 of n using which u have installed the linux and then press continue the update will happens.
** for text mode i will give u answer very soon coz i have to test it once again