MacBook update problem?

Hi i just bought a used MacBook from a friend i have been having a problem when trying to use the software update. it says in network diagnostics "network diagnostics was able to connect to the internet but not to the server "(not showing the server for privacy reasons)" This could be caused by problems with the server, or an internet problem between this computer and the server."

I pretty sure it has somthing to do with my friends job he works at thats why i did not supply the server name i just want to know how to change the setting to allow me to update my software from my home wifi thanks

Okay well i bought the laptop about 5 days ago and its excellent but on every computer at first it runs fast then it runs slow …when you restore a computer it runs so fast and then slows down again which is my problem.. okay well before you guys give suggestion i ALWAYS do a disk cleanup everyday and a degrag once a week and i tried CCleaner ..works like sh*** and ive bought Summit Soft System Tech Vista which gets rid of a lotta crap but still whats wrong with my intenet why does it slow down after about a week and i have Optimum Online with a Linsys Wirelss N Router. is their any secret files that i can clean in the Registry and their barely any programs on here so its very very cleaned out and its a 200GB hard drive and 3 gigs of ram runs smooth but i need help with the internet problem ..please give me some tips and trick thanks i appreciate it !! : )
And i have IE, and ive tries Safari fast but sucks cause doesnt work with java, tired firefox does the same thing as IE and ive tried Opera …they all dont work