How to retrieve/change a network password?

I have forgotten the password of my network.My lappy can connect to it directly when it starts.However, I need the password now since I've a friend at my place requiring to use the internet.I was wondering if there is any way to retrieve or change the old password? Please do reply.How to retrieve/change a network password?
if by network you mean router then you can always do a hard reboot. find a paperclip or something (don't use pencil's, the graphite can ruin your router) and hold it in for about 10-20 seconds till all the lights on the front go solid then re-connect to the router. the name will be different. you will need to re-do the set up configuration to secure your access point. if you need any further assistance e-mail me or use MSN live to contact me. Chemicle_26@hotmail.com