Techniques to manage storage spaces involve: determining an allocation rate of a storage pool based on a size of a storage space of the storage pool and sizes of allocated spaces for file systems from the storage space; determining a threshold allocation rate of the storage pool based on the size of the storage space of the storage pool; in accordance with a determination that the allocation rate of the storage pool is greater than the threshold allocation rate, determining a target file system from the file systems based on sizes of unused portions of the allocated spaces for the file systems; and releasing an unused portion of an allocated space for the target file system. Accordingly, the efficiency of space release of a storage system can be improved and the adverse impact of the space release process on the performance of the storage system can be reduced.