If these files are in the SMS environment, your sysprog can update the MGMTCLAS to set the value of the PARTIAL RELEASE option to YES IMMED. This sets RLSE as a default when files allocated under the MGMTCLASses you update are CLOSEd.
This is good option because you don't have to update the JCL, but it may have an improper secondary effect, for example if the MGMTCLAS you set to YES IMMED is used for DAM files, or for SAM files often used with DISP=MOD.
We generally give 'F' against datasets to free up unused memory.
Actually, you are freeing up unused disk space -- not memory. Terminology is absolutely critical to get right in IT since there are similar terms that may mean very different things. Memory is part of the processor where programs are loaded in order to run; files are stored on disk drives that are not part of the processor. Programs cannot run on disk; they must be loaded into memory first.