Wear your boots indoors to adjust to how they feel. Walk around, go up and down stairs, and generally just allow your feet to get used to the new sensation. Boots are much more supportive, and often heavier, than the majority of shoes, and this often means that even the most perfectly fitting boots feel uncomfortable at first.
Generally speaking, if you can walk around the house for an hour or two feeling supported, without any rubbing or pinching, then your boots are probably a good fit.
If you've gone through these steps and concluded that your boots don't fit properly, you can change them, as long as they are in a sellable condition, have not been worn outside and are within the agreed returns period. For more information, visit our returns page.