Use the API explorer to generate an link with your key and zip code. Use XML format. It will look something like this.
Don't pick any of the options, they're not used just enter your zipcode though you can enter zip code or latitude longitude.
Once you have that get the koboroot.tgz file here
Decompress it in a folder, it's a gzipped tar file so you'll have to find a tool for it for windows.
inside it is a file called weather.py, it's located at mnt/onboard/.apps
Edit it and find the worldweatheronline link which will be this
Delete everything from ' to the end like this
paste in the link you made
save it and then compress the mnt directory into another file named koboroot.tgz and follow the instructions on how to get that loaded into the kobo.
I am working on a clock that updates every second if I can figure out how to make the screen only refresh every minute and not let the script keep updating the weather every second.
Once I fixed it I ran the script that sets it up to update every hour. it will get a nice frame to hide the power plug and get hung in my kitchen.