Actually I would like to plot stress strain curve from raw data consists of loading and unloading responses. I don't know how to remove unloading data.
It depends on the software you use for plotting. Most software gives possibility to set limits for space to plot. And of coarse you can filter your data.
You can find a number of visualization software including open source one, such as VisIt or ParaView: https://en.wikipedia.org/wiki/Scientific_visualization