Chord Conversion

Hello Aiesh.

This song is in the key of G, so you can replace any Bm with the Bm7 from the G chord family. You can replace the D with D/F#. The A you may be able to replace with Am7 from the G chord family. Try it out and see how it sounds to you. In most cases this will work. If not, you can use A major, which is what is originally called for. Sometimes, songs break the standard rules and throw in a note not in the G scale, like in this case with the A major.
Hope that helps!