Learning the basic chord changes is something that a lot of beginners struggle with. Sometimes this is due to training to do too many new things, all at once.
New students often approach learning a song with new chords, by trying to play through the whole thing. Rather than playing through the whole song, pair up all the chord changes, and practice the chords in pairs, building lots of repetitions with each pair before moving on.
For example, if the song you were trying to learn is:
G Am Em D
Rather than playing the chords in this order:
G Am Em D
Play through them like this:
G Am G Am G Am G Am G Am G Am
Am Em Am Em Am Em Am Em Am Em Am Em
Em D Em D Em D Em D Em D Em D
D G D G D G D G D G D G
This method will be a lot more effective in helping you master basic chord changes, than trying to play through a whole song at once. This is just one of many techniques we use to help our students steadily progress with their guitar playing.