This question already has an answer here:
- Shimano shoe size 2 answers
I got a pair old Shimano SH-R133 shoes for my road road, they are size 46. I'm thinking about a pair of SH-XC30. Can I use the same size?
Just like buying sneakers or dress shoes (or really any piece of clothing/footwear), you can't just buy cycling shoes based on size, even within one manufacturer due to shape differences and size differences within a line (especially when going from mountain -> road or vice versa). Try them on and see how they work. If you can't try them on, you're going to have to do some guesswork with ordering and hope for a good return policy if the fit isn't good.
Even if they're the right size, you may find moving to a different shoe will make you more comfortable or confident, so you do have to shop around for them.