This is the situation:

About a month ago I went with a reseller, I created nameservers for my domain which the reseller provided, and all was good. I am in the process of switching resellers, but having some problems. Since I already created nameservers through my registrar (www.registerclub.com), which were ns1.hostingguys.com and ns2.hostingguys.com, and my new host has created the same names for the nameservers (ns1.hostingguys.com & ns2.hostingguys.com), I tried creating the same nameservers again but with the different IP addresses, and that was at least 48 hours ago, and nothing is happening, the domain shows up still on my old reseller. Would I need to somehow delete the old nameservers or something?

you have to delete or modify the old ones. normally modifying them by replacing the old IP's with the new ones would work.

Also, depending on your registar it could talk up to 72 hours.