You cannot resize raw files. But you can resize image files derived from raw files. Camera Raw offers to do the resizing right at conversion time (conversion from raw to JPEG/TIFF/PSD, that is).
Unfortunately, the Camera Raw resizing feature is crippled. First, it offers only a limited choice of a few pre-defined sizes. Second, it introduces unwanted ringing artifacts into the resized file (these artifacts are tiny so most users won't see them---but they are there, around high-contrast edges, and will get emphasized through subsequent sharpening).
Better convert your raw file to an image file at the native file dimensions (i. e. no up- or downsizing), then do the resizing in Photoshop (Image > Image Size). Use the resampling method Bicubic Sharper for downsizing and Bicubic Smoother for upsizing. These will yield the same results as up- or downsizing in Camera Raw but with free choice of target size and without the artifacts. Prior to upsizing, a small amount of sharpening for source often is beneficial.