Optimize house wifi range/speed - Netgear AC1750 modem/router + Orbi ac2200 RBK23

Need advice - I have Spectrum for my Internet (only getting 60-70 mbps upload speeds when I am paying for up to 200 mbps). I have Netgear AC1750 modem/route currently in 2000 sq.ft. home and we have spotty wifi. Trying to extend range and increase speed. I just purchased the Orbi RBK23 system to extend range upstairs (arriving this week).

Do I need a new modem??? I have had this modem for 3 years. 

It is supposed to support up to 680Mbps modem speed and Dual-Band AC1750 (2.4GHz & 5GHz) WiFi speed. 16x4 channel bonding/ Approved for plans up to 300 Mbps but I have never gotten close to this kind of speed.

Thank you!