If you need to buy new strings, here what you should know:
The only difference between the two (D and G) is the string gauge and the saddle (the compensation on the saddle is slightly different to improve the intonation).
The D has 2x.012, .016 AND 025 strings.
The G has 0.010, 0.023, 0.033 AND 0.047 strings.
Here’s some videos about string change and tuning: