From the datasheet.
Each of the PORTB pins has a weak internal pull-up. A
single control bit can turn on all the pull-ups. This is performed
by clearing bit RBPU (OPTION_REG<7>). The
weak pull-up is automatically turned off when the port
pin is configured as an output.
And
2: To enable weak pull-ups, set the appropriate TRIS
bit(s) and clear the RBPU bit (OPTION_REG<7>).
But I bet you want the other pins to be inputs also?