Extending visa

Hi, I'm Krizzy from Philippines and now in Sweden.. I only have 3months visa. I would like to extend my visa for more months. I would like to ask if what are the requirements to extend visa and how much it cost? How many months is the longest for extension? And where to go to process it?
I hope to here from you guys.. It would be a big help. Thanks.

migrationsverket.se/English/Private-individuals/Visiting-Sweden/Extend-a-visit.html