The best way to check the fit of a shoe is to try it on in your local bike shop before purchasing (hopefully you'll make the purchase in the shop too!). It is better to do this in the afternoon or evening as your feet can expand slightly during the day.
Shoe sizing is pretty consistent across brands, particularly when compared to other pieces of cycling clothing – but just because your old and worn-out size 46 shoes were comfortable, it doesn't necessarily mean you can jump straight into a different brand in the same size.
Arch heights, shoe widths, and different fastening systems can all mean that you may find yourself going a size up or down when buying new cycling shoes. Flashier shoes usually come in half sizes, so you can get a good match for your feet. Lower priced shoes, however, tend to be sold in whole sizes only - they are usually more roomy to start with as well. If your feet are between sizes, that can make choosing the right size tricky. IF you're not sure, we'd suggest sizing down.