Netgear Router wont put out my network speed through wifi!

Ok so a little while ago I upgraded to mediacom 50Mbps and phone as a bundle. Only problem is my router only has a download speed of around 10M, hasn't exceeded 20M. All my devices are G and I can't try N because its at 5Ghz and I don't have any devices that have that. I know G can put out more that what it is and I would like for it to be faster. My desktop has internet through the Ethernet which goes to the wireless router first and that gets between 40-50M. I have a Netgear WNDR3700 V.2 And its set for dual band so its broadcasting G at 2.4Ghz and N at 5Ghz. Please help, maybe I don't need the N turned on at that will help?? Any suggestions would be great! Thanks in advance.