Compiled answer by myself:

Get fresh link from: https://jdk.java.net/14/

Download binary:

wget https://download.java.net/java/GA/jdk14.0.2/205943a0976c4ed48cb16f1043c5c647/12/GPL/openjdk-14.0.2_linux-x64_bin.tar.gz

Unpack it:

tar xvf openjdk-14.0.2_linux-x64_bin.tar.gz

Move to jvm folder:

mv jdk-14.0.2 /usr/lib/jvm

Update java and javac alternatives:

update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk-14.0.2/bin/javac" 3
update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk-14.0.2/bin/java" 3
update-alternatives --set "javac" "/usr/lib/jvm/jdk-14.0.2/bin/javac"
update-alternatives --set "java" "/usr/lib/jvm/jdk-14.0.2/bin/java"

Use to switch between versions:

update-alternatives --config java

As correctly pointed out in the comments by RealSkeptic, the JAVA_HOME environment variable is not utilized by your shell to detect where the java runtime is located.

Try adding the following to the line to your environment file after export JAVA_HOME

export PATH=${JAVA_HOME}/bin:${PATH}

If your JAVA_HOME is set correctly it should be added correctly to your PATH