You can upgrade your WebSphere Application Server to newer version using IBM Installation Manager which is installed on your instance. In order to do it you will need IBM credentials.
You can do it manually using imcl command from IBM Installation Manager or automatically using RapidDeploy which is also shipped with the WebSphere product.
Simply import attached blueprint to your RapidDeploy instance - set your IBM credentials and deploy the project.
Our videos may help you configure this: