You can free space, but how that happens is not explicit.

The more people a file is requested by, the more places it is stored. If the file ceases to be requested, and all the participants decide to remove it from their caches, the file is gone.

DHT records are slightly more persistent, but without a sponsor they fade as the network's churn removes the nodes that once hosted them.

It is very hard to delete things, and the most likely things to be deleted are things people are not providing effort to preserve (even one person providing such effort is sufficient to maintain the DHT records.)