If you are using SVM or something like Veritas VM it is possible to resize your /u01 Filesystem.
The actual doing depends on your environment: SVM or VxVM? Do you need your backup slice, or can it be completely uses?
If you use SVM and don't need the slice where your backup resides thinks are quite simple:
use metaclear to clear your backup metadevice and use metattach to attach the now free slice to the metadevice you use for your /u01 device.
Then use growfs to grow the actual filesystem.
Be aware that any work on a running filesystem is a possible risk. So be sure to have a consistent backup of you database if anything goes terribly wrong.
If you need an extra metadevice for /backup, the way would be to destroy the metadevice and using format to resize the slice your backup is on. The free space can be used to create a new slice you can add to your /u01 metadevice.
This means that you loose all contents of your backup slice as you need to create a new filesystem.