Please share some ideas/methods/tutorials for clearing the CPU usage/kill processes through jail shell access at Winscp for reseller hosting.
You can't! Jailshell has limited access. You must have the root access to work with commands that matter with CPU.
If your server is overloaded and ram/cpu is high that's your hosts problem you can't do nothing about it, except move to a company that doesn't oversell and overload there servers, you can't do hardly anything in a jailed shell.