Your 2N6057 is an original. These are pretty tough - don't mess with him yet.
7.15 is the typical reference voltage for these but 723 regulators are pretty sloppy with their reference range and can range from 6.8 to 7.5.
You set the desired voltage at pin 5. The regulator monitors pin 4 and raises the output until pins 4 and 5 match each other (in theory).
Using your values: Vout = (7.07)(4770 / (2136 + 4770)) = 4.88V. You see 4.92 so that works out pretty close.
Your R8 is too low at 4770, lowest should be 4940 ohms. If you measured in circuit, this can mess with measurements.
But, yes - you can go up in resistance. 5.23K is the nearest standard value for a 1% resistor.
With your existing regulator and value of R7 then you should get:
Vout = (7.07)(5230 / (2136 + 5230)) = 5.02V
And note that the reference voltage can vary with room temperature as well as having a rather ingenious built in frustration detector.