From the IRS: There are no tax consequences if you change the designated beneficiary to another member of the family. Also, any funds distributed from a 529 plan are not taxable if rolled over to another plan for the benefit of the same beneficiary or for the benefit of a member of the beneficiary’s family.
You are eligible to rollover from another 529 plan once every 12 months without changing the beneficiary. Rollovers need to be made within 60 days of the distribution from the other 529 plan, otherwise the distribution will be treated as a non-qualified withdrawal.
@dcandmc is correct and, to add, you would want to contact the 529 plan or plans to ensure that any requested rollover was properly coordinated. None of it is difficult to do, you just want to plan ahead and make sure you have all your ducks in a row beforehand.