When a toddler has their diaper changed it interrupts what they are doing so they hate being pulled away from what they are busy doing to have their clothes removed and diaper removed for a new one.
The toddler may also hate having their pants removed in front of other people and may be getting to the age of getting embarrassed if you lay them down in front of others such as in public or in the living room and undo their diaper and wipe them and change them their.
When my son got to 3 years old he hated having his diaper changed especially if I tried to change his diaper in public or in our living room or in the living room of other peoples houses.
He would scream and try to run if I tried to remove his pants but he calmed down if I would first walk him to the bathroom or a bedroom in privacy and then changed his diaper their.
So you might try that by taking your child into a private room away from others and it be only you and the child when changing their diaper.
Also let them know when it's time to change their diaper so they have advanced warning about it.
For example if they are playing with some toys or watching TV go over to them about 20 minutes before the diaper change is to take place and tell them that it will be soon to change your diaper.
Then when the time is up go get them and take them to a room or lay them down to change their diaper.
Have the new diaper, wipes, creams etc ready to change them so you don't have to stop and go get something.