there is a whole chapter in the students guide devoted to this topic, there are several companies who provide this as a service . and there are quite a few hits in google if you checkout oracle to exadata migration. For you I would suggest logical migration would be the simplest method.
that really depends on the dependencies in your environment:
- Which plattform you come from
- Do you have a phsical standby as input
- Do you have to done a logcal migration while changing from another platform for example Windows
- How many time do you have for the migration
You need to do during the project setup a task to write a concept an then go into the details.
For more information I need more input from your actual environment