A lot will depend on where the cold spots are on your radiator.
If your cold spots are at the top of the appliance, there is a good chance that bleeding your radiator will help to allieviate the issue.
Follow the advice specified in our guide on how to bleed a radiator to get the job done.
Conversely, if your cold spots appear at the bottom the radiator, it may mean that you have an issue with radiator sludge - in which case you can learn about how best to deal with that kind of a problem, by checking out our guide to flushing your radiator.
If all else fails, we have an expert guide on fixing cold radiators that you are sure to find some help in!