Alternatively, if you prefer to use a JRE with an open-source license (GPL v2 with Classpath Exception), you may visit https://adoptopenjdk.net and install the latest Java Development Kit (JDK) for ...

For example, on Windows BiglyBT will usually install a Java 8 runtime in "C:\Program Files\BiglyBT\jre". BiglyBT will continue to use this runtime unless you rename/delete it. Oracle has stopped ...

The actual upgrading part isn't included in the document, but it will presumably be done through official methods such as Windows Update in Settings, the Installation Assistant, installation media ...