How do I only update the java runtime in a project? [duplicate]

Question

This question already has an answer here:

• How do I tell Gradle to use specific JDK version? 11 answers
• How do I change the IntelliJ IDEA default JDK? 8 answers

I won't have much expertise in this so I apologize in advance. Basically I have a dropwizard application (using IntelliJ) that uses Java 8 compile time and runtime.

I want to still have Java 8 compile-time, but want to upgrade to Java 11 for run-time.

Someone told me it's possible but it's sort of confusing to me. I downloaded the zip file from https://jdk.java.net/11/ and changed my JAVA_HOME env variable on my windows machine. But won't this also change my project to compile in Java 11? How does Java 8 compatibility work?