Can change double entry M visa to L type or F type??

I have a double entry M type valid for 6 months with maximum 60 days duration.. I have an single entry on it before around 40 days in but i need to stay for more than 60 days so I don't want to exit and then come back so can i extend the duration of stay or I should change it to another tourist type or F type so can i stay longer than 60 days with my first entry??? Is it possible?? Can kindly let me know thanks