Set size of view in NIB / XIB file

In the Attributes inspector, in the Simulated Metrics section, change the size to None. This unlocks the view and you can drag to resize it.

EDIT: As noted in the comments below, in more recent versions of Xcode you must set the attribute to Freeform, not None.

There is the solution for XCode 9.0

Select your view and set simulated Metrics as this :

After this, you can edit your view's size :

DEPRECATED :

There is the solution for XCode 8.1

Select your view and set simulated Metrics as this :

After this, you can edit your view's size :

Such settings:

makes me possible to change view size:

Xcode version: 5.1 (5B130a)