There's multiple ways you can go about this. You can put both in a timeline with upper field first. That way a pulldown gets added to you footage but retains the framerates. That way isn't my favorite. Only use this way if you need to retain the time of the clips for sync purposes or multi cam.
The other way is to reinterpret your footage. In premiere when something is in your bin you can right click it and go to modify. There you can reinterpret the framerate. What this does is reorder the
frames so the duration will change. Like if you're going from 24 to 60 fps, the clip will be shorter because there are more frames per second. Since it's such a mild change in framerate the audio should only change a little bit.