My nokia nuron holds 20 messages in the outbox, how do I increase this?

[youngpuertoricanblood]

my nokia nuron from tmobilee only will hold 20 messages in the outbox . if I send a message and there's already 20 in the outbox then it will delete the last message and add the one I recently sent so it always stays at 20 . my inbox holds a lot though. Help!