Just a friendly note in addition to what Kalyan already mentioned. Its NOT Worth to try to upgrade. It just won't work. WLS 6.1 is like 10 yrs old back software and is completely overwritten. Even the EJBs java code you used at that time is wothless now. Take the same requirements rewrite and deploy on a brand new latest weblogic server domain.
I happened to wok on much older versions of WLS like 4.5 where they had like 5 different servers for portal, campaign, core server and had concepts of pipelines etc. We rewrote the entire application which is far better investment of time and money. And it worked out pretty well for us.