You've fallen in love with the perfect pair of leather boots, only they're just a little too small. No problem. Fortunately, leather stretches a bit with wear. Depending on the condition and flexibility of the leather, it may only be possible to stretch the boot one to two sizes larger.
For shoes that need to be stretched less than one size, leather conditioner may do the trick.
Rub the inside and outside of the boots with leather conditioner. After they dry, wear them as usual and walk around as much as possible. Repeat the process as many times as needed to get a comfortable fit.
Spray the boots with a shoe-stretching liquid or spray. Apply a generous amount, concentrating on the areas you wish to stretch. While the boots are still wet, put on one or two pairs of thick socks to add bulk to your feet; use one pair if you need to stretch a small amount, and use two or more pairs if you need to stretch the boots substantially. Put the boots on over the socks and wear them for several hours, walking around as much as you can.
Using shoe stretchers with the stretching spray works best for boots that need to be stretched a full size or more.
Spray the boots with shoe-stretching liquid and insert wooden or metal shoe stretchers inside them. Adjust the tension to the stretchers so that they fit snugly inside the boots, and keep them in there for one to two days.
Remove the stretchers and try the boots on to see if they fit better. If they're still too tight, reapply the stretching liquid and put the shoe stretchers back in for another day or so.