How to increase network bandwidth of AWS EC2 instance?

We hosted a site in AWS EC2 of type c4.8xlarge. It is a fairly large system with lot of memory and compute resources. It incurred a planned heavy usage during a 2 hour time frame this weekend. While it did not crash, it slowed down quite a bit and failed to perform at the expected level. I was analyzing the stats and found realized that the network bandwidth is the main culprit. While the CPU usage stayed below 6%, the networkIn and networkOut seem to have peaked during that timeframe and thus all the problems. While I'm not an networking expect, some reading online seemed to indicate that all the traffic going through one NIC could be the main source of limited network bandwidth. Is this true? Would hosting the site on a different type of EC2 instance help increase the network bandwidth? Here is how the networkIn and networkOut metrics looked like under heavy load.