It's unlikely that Ford Ranger rims will fit a Jeep Liberty without modification, and even then, it's not guaranteed to be safe. While both are trucks/SUVs, the bolt patterns (number of lug nuts and their spacing), center bore (the hole in the center of the rim), and wheel offset (how far the wheel mounts in/out from the hub) are likely different. These dimensions need to match exactly for a safe and proper fit.
You'll need to check the specifications of both the Ford Ranger rims and your Jeep Liberty's wheel hubs to compare these critical measurements. This information is usually found on the wheels themselves or in the vehicle's owner's manual. A local tire shop can also assist in verifying compatibility. Trying to force mismatched rims onto your Jeep is dangerous and could lead to wheel failure.