Method 1:
This is for video right? (i’m guessing because of the size) Make a new file, using the video preset that matches your settings (I think in your case it would be PAL D1/DV, 720×576 (with guides)). Then drag your logo into your new psd file and scale it down until it fits, using shift to maintain ratio. Then Flatten. save as psd. (if it has a transparency, you can make an alpha channel and have a completely flat psd, much smaller size) or just leave the transparent logo on it’s own, delete any empty layers.
Method 2: Crop it…
go the the crop tool… there should be an option to enter your exact pixel width and height… then select the area you want to crop, hit enter and viola. it will scaled down everything… But I think the 1st method is best because of the pixel aspect ratio.
Make sure you save-as so you don’t save over your original.
C.R.