There is a simple way to connect your .is domain to a website hosted by Wordpress. If you have a 3rd party DNS hosting, see instructions here.
The first step is to set up your domain on Wordpress’s nameservers. You do this with a method they call “Domain Mapping” - see instructions from Wordpress here. At the end of this process, they will tell you which nameservers to use, normally these three: ns1.wordpress.com, ns2.wordpress.com and ns3.wordpress.com.
The second step, is to redelegate your domain to the Wordpress nameservers, using the isnic.is web interface: