Well it is not everyday that we change DNS nameserver. We can understand the confusion if you do not know what is DNS nameserver, let alone change it at the what,..domain registrar? Most of the big domain registrars do have their own tutorial that is very clear and precise, complete with the screenshots, like GoDaddy, namecheap and local ones like Vodien and Exabytes:

namecheap https://www.namecheap.com/support/knowledgebase/article.aspx/767/10/how-can-i-change-the-nameservers-for-my-domain

GoDaddy https://sg.godaddy.com/help/set-nameservers-for-domains-hosted-and-registered-with-godaddy-12316

Vodien https://www.vodien.com/knowledge-base/articles/update-nameservers

Exabytes https://support.exabytes.sg/en/support/solutions/articles/14000031330-update-domain-nameservers-via-client-area

So, here is the 4 step IDIOT-proof guide for SMART people who know nuts about changing DNS nameserver. The following tutorial screenshots are from VOOJU  (their FAQ is, er, not so comprehensive, a few-liner with absolutly NO images, that explains why this is based on VOOJU)

Step 1
After logging in, click on MY DOMAINS on the left hand side

dns vooju1


Step 2
a. Check on the domain name to select
b. Then click on the first button at step 2 "Update Nameservers/Park/ URL Forward"

dns vooju2

Step 3
a. Replace the current
NS1.OROSHINHOSTING.COM with ns1.c35675.sgvps.net
NS2.OROSHINHOSTING.COM with ns2.c35675.sgvps.net

dns vooju3

Step 4
After clicking on update, you should see as follows, 

dns vooju4