With age, gravity tends to give us a larger foot size. Our feet expand under our weight.
I have a couple of pairs of expensive (well, expensive for me) and highly-durable Brooks Brothers loafers which I am loathe to part with but are no longer comfortable. 20 years can do that. Mrs. BD says I am silly not to replace them, but I tried some tricks of the trade first. It is not unusual to be like me, with feet of slightly different sizes but who will not spend the money for custom shoes in London.
Solid, well-made leather shoes can be stretched between a half-size to a whole size. Inexpensive shoes can not take the stress of stretching - either the leather itself, or the stitching, will break.
Things to try:
Shoe stretchers will adjust width or length. Cheap on Amazon. Over a day or two, you keep increasing the tension in the stretcher. Heating the shoes with a hair dryer or in a hot sun makes the leather a bit more stretchable.
Wetting the shoe well with water or, better, isopropyl alcohol (rubbing alcohol) before stretching is what expert cobblers do.
Simpler, soak some heavy socks with water or rubbing alcohol and wear the shoes. If sitting, it should be painless.
Results of my experiments with these? Be careful not to overdo it or you can end up with loose shoes.
Other ideas: How to Stretch Shoes That Are Too Tight