Need help with IM app called "Line" on Windows 8

I am using a chat app called "Line" on my Windows 8 laptop. An issue I have, however, is that I cannot figure out how to decrease the size of the chat window. It's always fullscreen and I can only see options to either minimize or close the app in the upper right-hand corner when there is usually also some sort of "restore down" option to shrink the window. It's quite irritating because I wish to multitask while using this app and in every other aspect it perfectly fits my needs!