No – you can change the investment funds you hold, for free, up to 15 times per year. And if you are changing more than one fund holding, it still counts as just one change if you’re doing it at the same time – so you can completely change everything your hold in your portfolio if you like, with up to 20 different funds being bought/sold at the same time, and it still only counts as one of your 15 changes.
If you want to trade particularly frequently, you can go beyond 15 trades per year, at a cost of USD/EUR 22 (or GBP 15) per trade for anything more than the 15 free trades – and again multiple trades done at the same time count as just the one trade. Your "trade count" resets to zero every year on the anniversary of your account opening date.