Tab on the wall you wish to edit. On both ends you will see nodes - you can drag them in any direction to change the wall’s length or position. To enter an exact measurement, select the i-button:
The wall’s Property Inspector will open. Choose from which side of the wall you want to increase or decrease the length. To change the direction, tab on the icon showing a wall with an arrow.
Next to it you can decide whether or not you want to keep a 90° angle when the new wall length is applied to your plan. Bellow are two examples of how the same plan changes when the right angle function is off and on.
As an alternative you can tap on the measurement to enter the length directly.