The latency between you and your EC2 instance is decided by three factors. The first is the speed of light - this is not something you can do anything about.
The second is the delay caused by the last mile access, and depends on what kind of technology is used. Cable? Ethernet? (See three)
The third is the path your packets take over the network. This is something you MIGHT be able to do something about, but most likeley it would require you to switch to a different service provider with better routing towards the EC2 instance.