Depending on BIOS you may or may not be able to overclock.
Perform a clean install after backing up data to an external drive or cloud storage... Most slow downs are caused by running the same build for too long without a rebuild. After a rebuild it might feel like a totally new computer.
If your trying to run new software and your computer barely meets the requirements there is not much to be done, however a SSD drive upgrade from a HDD can make for faster load times. SSD's are cheap but some Mac's are tricky with drive upgrades.
*** What is running slow with your Mac?
