@Musashi_Fujimura
Ways to unsinatll Java or any software from a computer machine is :
From Mac : https://www.wikihow.com/Uninstall-Programs-on-Mac-Computers
From Microsoft : https://support.microsoft.com/en-us/help/2601726
From Linux : https://www.howtogeek.com/229699/how-to-uninstall-software-using-the-command-line-in-linux/
In winodws computer if you want to uninstall press (Windows Key + r ) at same time then type appwiz.cpl in run box and click on OK. You will see control panel there. And then you can uninstall software from control panel.
After uninstalling Java you need to restart your computer it doesn't matter that which OS(Windows / Linux / Mac) are you using, You need to restart your computer.
Then install Java 8 which is stable for ODK from below link
http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
Narendra