The drive should slide away from the connection to the motherboard. If the drive doesnt slide away from motherboard connection look for a bracket that is keeping it in place from disconnecting. Once its disconnected you might have to remove a thin metal hard drive housing bracket. Move this hardware to new drive, and slide the new drive in the way the old slid out. If there was any locking hardware place the hardware back. Put the laptop back together the way you removed it ( Making sure that the screws removed are the correct length for each hole they came out of ) * If a screw that is too long is added to wrong screw hole you can damage the laptop or destroy it.
