Hi @alaminbdd5571ec

DigitalOcean is an unmanaged platform, meaning they are only responsible for power, hardware, internet and a few other things. Whatever you install on the server is your responsibility and you have to make sure it’s updated and configured correctly.
If you need more help, then you need to hire a system administrator.

That being said, you really should consider upgrading your CentOS to something newer, since version 5 has been End-Of-Support for 2 months - and giving the latest critical sudo-vulnerability, it leaves your servers in a bad state.
https://en.wikipedia.org/wiki/CentOS#End-of-support_schedule

You can follow this tutorial to set your kernel to GrubLoader, which will then load the newest kernel installed on your CentOS:
https://www.digitalocean.com/community/tutorials/how-to-update-a-digitalocean-server-s-kernel