At the moment, you’re likely making at least 1 chord by putting one finger down at a time (likely the G). What I want to introduce is making the shape of each chord before putting your fingers down. This will lead to MUCH quicker changes, and is how the pros do it!
'Air changes' Exercise
Make the shape of e.g. the G chord a cm above the fret board and keep your fingers still in this position for a few seconds
Press your finger down and strum the chord as usual
Lift your fingers and repeat this between all the chords you know.
It helps to always go from the one your struggling with (likely the G) between everychord. e.g. G to D, G to Em, etc.
The idea is to implant the chord shape into the muscle memory of your hand. This is much better than just remember which fret and strings the fingers go into and will make your changes easier and faster!
Here's a video which demos the C to G change in more detail.