Freezer is working OK but fridge is warming up -

Not likely. Assuming you have tried adjusting the temperature control, a more likely suspect would be a problematic evaporator fan. This fan is located (usually behind an access panel) in the freezer. Its purpose is to move cold air throughout the freezer and the refrigerator. If the fan fails, there may be enough cold air to keep the freezer cold; but there is not enough to keep the refrigerator at the proper temperature.

If the fan is running, you should be able to hear it. If you can't, open the access panel and look at it. If it's not turning, you likely need to replace the fan motor.