How to increase size of pattern

How-to Questions
1

Hi
I have a baby pilcher/diaper cover pattern size 0-3 months in Double Knitting yarn.
I would like to make it in size 3-6 months or 6-9 months.
Needle size is 3 1/4mm (UK) and 4mm (UK) needles. Tension 28 rows to 22 sts over 10cm x 10cm (4" x 4") square knitted in stocking stitch.

To make the next size up would I have to change the wool to a thicker wool such as Aran or 12 ply e.g. or change needle sizes.

Thanks in advance.

2

You could try knitting it with heavier weight yarn and bigger needles.

3

Thank you. I will try that.