How to lose weight?

I've always been fairly ordinary in terms of weight. But since my 50s my weight has crept steadily up. I'm now well...quite a bit larger and over the past year or so I've been trying to lose a bit of weight. I look after my grandsons twice a week which is exhausting and I think I'm quite active those days. I do one Pilates class a week. I do have a sweet tooth so am trying to have fruit instead and save treats for the weekend (although occasionally I'll share my boys' treats . Does anyone have any good tips? Does the 5:2 diet work? I hate gyms.