This is not OS 9. There is no need to do anything about your memory. The system manages it automatically, and puts it to its best use.
If your system is slower, it is not because memory is being used. It's slower because the CPU is being used--check your Process Viewer. Perhaps you have some tasks running that you didn't know about.
"sudo periodic weekly" frees up RAM by forcing the virual memory system to page memory to disk, then when its tasks are done, the memory is free. But this free memory is a red herring, because next time you need to contents of the pages that were moved to disk, you have to get the data from the hard drive instead of RAM.
Restarting the computer would be equally as effective for freeing up memory. So would quitting all your running programs. But those answers are just as silly as running "sudo periodic weekly."
Chris