sure, no problem. But synthetic is better in every way.
Going Synth to dino is probably easier since going from dino to synth has a nasty way of letting you know if you have any leaks...
Synth is far better than dino, but dino is more forgiving.

At the same time I suggest staying with synthetic oils if thats all thats been in the engine because different oils cause components to wear in a small but different way.