I am not sure of you experience level, so I will give a simple explanation.
In general, you will need to add a disk or remove existing software. Cleaning up your /opt directory, is tricky because that is typically where your applications load.
The best advice is to add disk. If you can't do that the only other way might be to take a backup of your root OS volume and re-install your OS and give more space to your /opt.
The ideal way to do a system is have separate volumes for /, /var, /opt, /usr, and /home. This way you can do exactly what you are asking without affecting the OS.
