You can't upgrade camera raw, but you can use Adobe's free DNG converter to convert the raw files to DNG. Once they are in DNG format, you can import them with your older LR installation.
Lightroom doesn't use the Camera Raw plug-in. Everything is part of the Lightroom program. If your camera isn't supported in the version you are using you will either have to upgrade or use the DNG converter.
Like Canon, Nikon uses the same file extension for all of the different camera file formats. New formats require new software to read them.
Most likely you have a newer NEF file that your old LR software cannot read.
Your two basic options are to (1) convert the NEF file to DNG using a newer version of the DNG converter, or (2) upgrade your old LR software to the current 5.7.x version.
Thank you for your responses. I was able to convert the .nef to a .dng and import. I have one follow-up question. When I go to the develop module and try to choose a different camera calibration profile, all I get is "Adobe Standard". Is that normal?
If it is a NEF file there should be several different profiles available for it. What camera took the picture?
The picture was taken with a Nikon D810. My version of LR does not support the nef file. In converting it to a dng, I was able to import it to LR but I can't seem to change the camera calibration profiles. Maybe, I lost that ability when I converted to dng or maybe it's because my version of LR does not support the original nef file...?
NOt sure which one is troubeling you.
As soon as you convert from RAW to some other file system, things are locked, so you only have the possibility to create a preset in lightroom that fits what you're expectiong to receive.
In many cases it makes more sense to shoot in jpg and get the Picture Style right in the camera, you have many options in the D810, as a D800-user I know.
The reason I upgraded to LR5 was also the change to the new D800.
You will have a better and faster workflow in LR5 with the big files and some better possibilities than in LR4 ...
The upgrade to LR5 is not as expensive as your D810 was
Many people are selling their key for less than 50$ ... I think this is quite fair and saves you a lot of time(=money) as you will be stuck in the DNG-workaroung in future for every RAW you shoot.