Hi, currently i have a 30days single entry L visa.

I will be flying into Shanghai on 15Aug, then Dalian on 18Aug. Will return to shanghai on 13Sept, which is 30days from the day i arrive. Now im thinking of staying for a couple more days,maybe even a week. Should i get an extension on my current one, or reapply for a new one? if reapply, what are the options available to me? multiple visits? number of days? And where should i get the application in Dalian? should i go through a agency?
Many thanks in advance.