If you are using the community edition you can donwload the versions provided by the download pages Downloads · WildFly or old versions here JBoss Application Server Downloads - JBoss Community.
This is mostly a complete new installation. For community versions there are no patches. If you need updates, security fixes and patches for such versions you need to buy a subscription and use the EAP (enterprise version of JBoss). Here you will get patches according to the support policy, see subscription-value and support-policy