Try whois myhost.net
- this will tell you the domain registrar that's managing your domain name records.
Log into that domain registrar's system and change the domain name servers for your domain through their interface.
If you are trying to use DNS servers whose names are inside the domain they're serving (e.g, if the DNS servers for myhost.net are named something like ns1.myhost.net instead of ns1.somethingelse.net) then you will need to include "glue records" that provide the actual IP addresses of your name servers - otherwise you'd have an infinite loop of lookups (e.g., to resolve www.myhost.net, you'd need to talk to the server at ns1.myhost.net, and to get that address, you've gotta talk to ns1.myhost.net, ad nauseum)