top output that you posted it is clear that you have only 16 megabytes of free RAM.
There is no single process that is using your RAM - GNOME starts many components - and most of the processes that are visible on list comes from GNOME session.
I see two solutions:
- remove X and use console only environment
- install some lightweight WM
Depending on the purpose of that VPS you should choose solution. If you want to run on it some services that doesn't need X, and you installed X and GNOME to "simplify" management just remove it. Install
mc for file management and
nano as editor.
If X is required to run some software on VPS remove GNOME and all stuff installed by GNOME (you have
cups running on server - it's unnecessary unless you have printer connected to VPS ;)) and install some lightweight WM like