You can find the particular image size of every image on the image detail page. You do not even need a free account to see this image size details.
Just click on any image you like to know the resolution and print size for
Scroll down until you see the 'Image Specification:' area
Here you can find the specific file size and resolution information about that particular image.
Keep in mind
The file you download will be in JPG format, therefore it do NOT have the 50MB in size. This size is uncompressed and if you would i.e. use it in TIFF format
If the 'Maximum Size at 300dpi' do not show your print size then you should still be able to print the image without any major issues. This is just a calculation for the perfect image print size. Therefore you do not need to worry much about that size
Every downloads counts agains your download credits. We highly recommend to always download the highest resolution. You can easily resize the image later with even included software on your computer