If you have words that you have grouped together and want to change the size of them, all you need to do is click on one of the corners of the grouped objects and drag it to the size you want,
Clicking on the corners will keep it in the same aspect Ratio,
If you want to skew the font size, then pick one of the circles in the middle and drag it,
For ungrouped fonts (and or other objects) you can also select them by holding the shift button on your keyboard and select as many fonts (and or other objects) and do the same as above,