Stage 2 Milk Formula

Possible to change to stage 2 formula for my 4 months baby? She's been declining and drinking less with her current stage 1 S26. I can't change other brands as that's the only brand she's suitable with. She has shows interest with solid foods. I've fed her yogurt and mashed potatoes too and she likes it. Can I change to stage 2 as soon as her stage 1 formula finished?