You do not need to clear your RAM cache. Linux has many decades of excellent memory management design built-in and will automatically free cache memory as memory pressure increases within your VPS. You can trust that Linux will release cache as necessary and won't let the system run out of memory just so it can continue to store things in cache.

The cache is a good thing and improves the performance of your VPS by using unused memory to buffer frequently-accessed files.

Clearing it will not solve any real or perceived problems. 

More info and proof of concepts available here: https://www.linuxatemyram.com/