extand my stay for few weeks

i am planning to come to japan this summer for a summer program which lasts for 6 weeks (mid june to early august), and i was told that i need a short term study visa that expires when the summer program ends, but i would like to stay for three or four more weeks as i would still have summer vacation up until early september, so i would like to know if there is anything i can do to extend my stay there for three or four more weeks such as going there with a student visa from the very start or switching from a short term visa to toursit visa that i would allow me to extand my stay there, any information regarding this matter would be greatly appreciated.
best regards,