How to attach parts of one model to another i have a 3d model, i want to swap it's feet and head with another 3d model. 
i imported both models, selected the parts, moved them to the desired position, pressed control + j to merge them.
but now it looks weird, it's so obvious that the feet doesn't belong to this body


i tried to fix this in sculpt mode but ended up making it look worse, so sculpting is either a wrong tool for this situation or i don't know how to use it currently.
can someone Please help me fix this problem?
thank you
In your case you can delete a lot of useless edge loops on your foot, you'll have the amount of vertices that will allow you to make the joint with your leg. As long as you choose the good edges it won't affect the shape of your foot. To do so you'll have to dissolve some edges, use the knife to create some edges between vertices, and at last merge the vertices of foot and leg. And don't forget to delete the face on the bottom of your leg.