Help with Escort Encore

I'm hoping someone here will be able to help me. I've just bought a 1995 Ford Escort 1.3 Encore and I'm having a problem with the front passenger door. The door will lock using the key but will not unlock and I can only open it from the inside. I wonder if anyone here knows what the problem is and if I can fix it myself (I don't have much experience with cars so the "fix" would have to be simple LOL), or if I will have to take it to the dealer?

Thanks so much :-)