PrettyVacant is right. The premium resources are near the top of the page in the resources sections.
However (... and I suspect this might be the problem ...) there are only premium resources for some subjects, not all. So if you wanted premium resources for a subject for which they do not exist, then you may be forgiven for thinking the premium resources are not working.
I think a message should be given for the subjects for which no premium resources exist, like:
"no premium resources here yet"
- or
"premium resources will be here soon", - etc.
Whilst this may disappoint, it will at least allay potential confusion.