The dash lights on my 2010 Pruis can barely be seen in the daylight. Is there any way to adjust since they are already turned up all the way

I am not familiar with the model but there are a number of ways instruments can be illuminated - a variety of standard incandescent bulbs being a favourite for manufacturers. That type of bulb is a vacuum type that will sooner or later become silvered or blackened resulting in a much reduced light output and an increased bulb temperature that if left unattended can destroy the plastic surrounding the bulb.

A few manufacturers have used a single light source and fibre optic strands to transmit the light into the instruments. The light source was often a vacuum incandescent bulb but could also be an led.

Leds are more common in modern cars than bulbs and are a low voltage device and so either a voltage regulator must be employed to supply the correct voltage to the leds or the leds could be daisy-chained in a series circuit and supplied by battery voltage or a combination of both.
In this case a tired regulator or a tired resistor or other components could lower the voltage supplied to the leds or in the case of a series circuit, a failed led will put an entire circuit into darkness.

I strongly suggest you obtain a wiring diagram prior to starting work so you know what you are facing...