1. Switch to layout mode,
2. Select your field,
3. Open the inspector (Mac: [CMD]+[I]),
4. Switch to "Position"-Tab in the inspector,
5. Click the locks as you like (e.g: right and top lock to pin it to top and right side; all locks: field height and width will be increased/decreased while resizing)
They are called "auto-size anchors". Select just the right anchor (lock) and the object will slide to the right as the window width is increased. Select both left and right anchors and the object's width will increase as the window width increases.
Duplicate the layout and play around with the anchors. This way if you get too far down the rabbit hole you don't have to figure out how everything was originally set. Also discover what it will do when no anchors are selected.