Use the latest Installation Manager, 1.8.9, for installing or updating WebSpheree 8.5 or 9.0. After downloading and installing WebSphere 8.5.5 or 9.0, you should update WebSphere to the latest available FixPack level ; FixPack 126.96.36.199 for WebSphere 8.5.5, or FixPack 188.8.131.52 to for WebSphere 9.0, so that you have the latest fixes for WebSphere defects, including migration related fixes.
Installation Manager 1.8.9
Recommended updates for WebSphere Application Server
Afterward, you should execute the WASPreUpgrade.bat/sh script from the /bin/, in the WebSphere 8.5.5.x or 9.0.0.x installation, to generate the backup of the WebSphere v7.0 profile. The next step would be to execute the WASPostUpgrade.bat/sh script from /bin/, in the WebSphere 8.5.5.x or 9.0.0.x installation, to transform the .xml file format from the WebSphere 7.0 environment into the format for the later version, then deploy the applications from the 7.0 environment, in the new environment.
Please review the following informative developerWorks blog:
WebSphere Application Server Migration Guide
As well as the following comprehensive reference:
WebSphere Migration Knowledge Collection: Planning and Resources
Click on the WebSphere version to which you are migrating.