The top of the foreskin is red and tight.
Can you give a bit more information? Were you doing something prior to noticing this problem that may have caused it? (Maybe unprotected sex, or vigorous masturbation). If not, maybe it's just an infection that requires some cream. This could be bacterial or fungal. Try a cream (obtainable from a pharmacy) closest to your own assessment for a few days, if no improvement, try a different cream. As long as you can urinate, there is nothing to be alarmed about. These things pass. If neither cream works, go to your doctor.
As Pepasan suggests, I am also wondering what was happening before you got the swollen foreskin! Have you always been able to retract your foreskin to reveal the complete glans / head of your penis? Perhaps, we are presuming your age?! Are you sexually active {age I am getting at, again}? If you have a tight foreskin anyway and you were trying more forcefully trying to expose more of your glans than usual, then, the outcome could quite easily be that the head area of your penis has become swollen as a result?!
Could you please take a look at the more recent discussion I have raised. It has more details. Thank you.
Could you please take a look at the more recent discussion I have raised. It has more details. Thank you.