How to decrease resolution from 1920x1080 to 720? I have After Effects CC running on Windows 10.

I have this template with resolution of 1920x1080. After rendering with this resolution my video player keeps on buffering, possibly because the resolution is really too high.

So when I try to render, where settings should I go to change resolution?
I would reccomend downscaling after, maybe using handbrake. Also, when you upload the video to YouTube, it may just be your pc that lags.