You may need to ask the seller a few questions...

Sometimes the kiltmaker is nice and keeps the extra material in the under apron (they double back to give it double thickness). If they did on THAT kilt, you can use that material to make an extra pleat or two.

OR... simply ask them if there's any overlap of the 2 aprons. If the top apron covers the last 2 pleats on the right hand side, then it can probably be altered relatively easily.

If there is NO extra material and NO extra pleats, it's up to you... the kilt CAN be altered to fit you, but you may have a flat section of under apron showing on the right side. If the buckle on the left hip doesn't reach (go through the leats and strap to the buckle on the left hip), you have 1 option (not the BEST option, but it will work). Add a "jumper" piece of material between the end of the under apron and the strap. Maybe use some STURDY cotton twill or cotton duck and double/triple it up for strength.

Talk to your local taylor and have them do it if you can't.