If you decide to switch brands or stages, you'll want to keep a couple of factors in mind.
If you decide you want to change your baby’s formula milk to a different brand or stage (e.g. from infant to follow-on milk), or even if your current brand launches a new formulation, there are a couple of things to bear in mind.
First is the type of formula milk your baby is currently drinking. There are four main types of formula milk: cow's milk based, goat's milk based, soya-based and hydrolysed protein formulas. Unless you've been advised by your GP or health visitor to switch from one type to another (usually because of a suspected allergy), you'll probably want to stick with the type of formula you're already using. For most parents, this is a cow's milk based formula.
You'll also want to consider your baby's age. If you've already started weaning, the transition from one formula to another can be quite quick. Try changing one feed on day one, followed by two feeds on day two, and so on until all feeds have been changed to the new formula.
If your baby is still only having milk, the transition may take a little longer. To start with, switch just one feed on both days one and two, and then switch two feeds on days three and four, and so on.
If you are changing to a different brand, instead of just a different stage of formula, you may want to swap as slowly as one feed every 2-3 days to allow your baby time to adjust to the new formulation.