LetsHost use a number of different sets of nameservers – which set of nameservers you use for your domain depends on your setup. Generally, if you have a hosting account with LetsHost, you should refer to your ‘hosting account welcome email’ for the correct set of nameservers to use. If you do not have a hosting account with LetsHost, you should use the nameservers ns9/ns10.dnsireland.com.
If you are unsure after the above, or would like to double-check all the same, please submit a ticket via your Client Area.