[otrs] Hello and first question

Hi, my name is Santiago Lunar and new using OTRS, i'm from Venezuela and work with Debian GNU/Linux since 2003; i think OTRS is a great Trouble Ticket system; i work as a server administrator in my country and I've already configured my OTRS but have a doubt and hope you guys could give me a hand. The thing is that i want to delete some items from the main toolbar because i don't want the users to use some of that features like i.e Phone-Ticket. What should i modify for making this items disappear? Please let me know what kind of info do you need. I'll give you all the info you need.