replacing words ?!?!?

[HaLaBi]

hello,
i want know how to replace a word with another,, or a sentence with another sentence, of cource in Mysql table,, using php..
for example i have "hello people" in all my records in the table, and i want to change it to "hello mates",,, how do i do that using PHP...??
thanx alot ;)

[Admin]

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[HaLaBi]

i quess this is not the only php forun in planet earth....

any way thanx alot...