Direct upgrade to 11g is not possible if you are on 8i.
You will need to migrate to an intermediate version first. In this case you will need to migrate to 10g release 2, and then to 11g.
The upgrade could be made in one of the following ways:
– DBUA (Database upgrade assistant)
– Manual upgrade
– Export and Import
You will need to choose what method is better for you.
Have a look at the Oracle® Database Upgrade Guide – 11g Release 1 (11.1)