Tj's half right and half wrong.
How new or 'modern' the boots are is irrelevant. Whether they fit or not is important.
Just because your boots used to fit doesn't mean they still will. Your feet can change shape over time.
Your old boots may need some care - get some leather restorer on them if they're looking dry and so forth. Wear the boots a few times for short walks and let them soften up and take the shape of your feet again - your feet may also need to toughen up a bit if you've not been doing much.
If you don't want to buy new boots and are still getting blisters, stick compeed or something on nearer the time of the walk, but not yet - give your feet get used to things first.
You don't want really tough, hard and dry skin, so ignore the whole surgical spirit thing. This either doesn't work, or causes skin to split/rip off in chunks. Not ideal.
And yes, I have, and still do occasionally fit boots for a living.
Angeldust - I'm sure there will be boots that fit or can be altered to fit. At a complete and internet diagnosed (and thus useless) guess, you may have wide feet and be sizing up to get the extra width, or you have issues with feet elongating when weighted. Wearing a size too big can cause as many problems as it may seem to cure. You can get some custom-made ones if you're really desperate.