4 wheel drive

I just inherited a 1987 blazer that is in great shape with the exception of a little rust. Anyway, the vehicle sat for many years before I got it but it started right up and ran great. I was trying out the 4 wheel drive unit. It went into 4 low, neutral, 4 high fine. The problem is when I shifted out of 4 high to 2 wheel drive the lights on the panel diagram stays on showing it still has front wheels engaged. The 4 wheel light as well as the other lights on the panel are all off. I can tell by the way it sounds and drives it is hung up in 4 high. How can I get it back to 2 wheel drive and will this happen every time I shift into 4 wheel mode. Any help you can offer will be gratefully appreciated. Thank you.