If the boots are rubber boots, it is best to buy new riding boots for wide calf. It is not worth having these boots altered. For leather riding boots, as long as they are not too old it is worthwhile having either elastic inserts or zips fitted. These can be inserted at either the back or the front of the boots, though they are obviously more inconspicuous at the back. You can choose between short or long zips that run down the entire shaft of the boot. You will need to have this work done in a specialist shop. It's not cheap, but it's still cheaper than buying new leather boots. If you have zips fitted, you should choose the long version. It also makes it easier to put on the boots.