Cut up a pair of old thickish socks, or use bandages, and have them ready. Give the boots a good soaking with leather expander (which you can buy from shoe repair shops etc.) round the tight bit - inside and outside the boots. Then immediately put on the socks or bandage, to make the top of your foot bigger than usual, and force the boots on. Walk around wearing the boots until they are quite dry - the longer the better. This should stretch them satisfactorily. Carry around the leather expander with you, to give them a good spraying if they start to feel tight again.

I can vouch for rubbing alcohol , if you buy some its called Isopropyl Alcohol , I got mine from ebay mix it with water in 3 parts water 1 part alcohol mix and spray it all over the leather . My boots were beautiful fine expensive calf skin red leather knee high boots and this worked a treat . I just put them on after i had sprayed them and gently pull the zip up stretching the leather bit by bit as I went , if it dried out i reapplied and got the zips up eventually and just wore them round the house for a while. Worth a try but it seems to work , I saw a video online with a cobbler describing the same process but with a calf stretcher in his workshop.

Get two water tight bags - insert them into the boots, fill with water and secure the top - pop in the freezer - honestly it works a treat!

you can take them to the repairers and they can stretch them for you otherwise damp newspaper could help but to be hounst if they are too tight to wear they don't fit

Wear a big pair of socks, put the boots on and heat them with a hairdryer till the leather is really quite warm. Walk around in them a bit till the leather cools. Do this several times and the leather should stretch.