Help! Pattern yarn and needle size change

Hi to all.
I need help please! I’m new to this but haven’t exactly started out on the right foot.

I’ve got a Rowan pattern for a hot water bottle cover that I’m using Sirdar yarn for (as recommended to me by my local shop as an alternative given the tension). My sirdar yarn suggests a needle size of US 9 which is fine but I have 2 needle size changes in my pattern had I used the Rowan yarn (US 8 for the front and US 6 for the rest). How do I accommodate these changes given I’ve changed yarn now?



You generally use the needle size in the pattern to get the gauge (sts/inch) it needs to be the right size. With this project it’s not as important, but you can go down one or two sizes for the smaller needle.

Thank you so much for your help. Fingers crossed it goes ok!!