How to change forgotten password?
 

i'm actually new to linux and i'm using Red Hat 5.0 while installing i can't remember if i was asked a username but i was asked a password unfortunately for me i can't login in fact the line for the password doesn't even write down the letters i give it!!please i really need help

The password characters disappear on purpose, it's so people can't look over your shoulder and see how long the password is.

Do you remember the root password? If so, log in as root and then run
If you forgot the root password, then I recommend you search these forums for "forgot root password". That question has been answered many times, and probably better so than I could answer in a hurry.