ALM uses disk space in 2 ways:
- Repositories related to Projects.
To alleviate space taken by logs (see path from Site Admin - Servers tab), can purge old logs (manually or via rolling log deleting script).
As for Repository, each project has it's own, and could be saving various artifacts like test screenshots, videos, scripts, etc. They could also contain various files related to testing notes or requirement documentation.
Some test results might be able to be "purges" by purging old test runs:
Then can run repository cleanup.
You might also can back some space by running repository realignment.
If your tests are using UFT integrated with ALM for automated testing, they might have too much detail being stored in ALM (videos of testing vs screenshots related to errors). Videos will take up much more space in the project repository.