How can i delete a wireless connection if i made a new one?

i have the Linksys wireless home router, and my sister made a new connection. The connection name used to be Linksys_O but now its a different one that my sister made. Everything (PSP, Laptop, and XBox Live) had to connect to a new connection. But how do I delete it to make it back to Linksys_O? I can connect to the internet on my PSP with the Linksys_O connection, but since my sister made a new one, i cant connect to it anymore. please help me because i wanna get back to the internet in my psp. Thank You