Hi guys sorry if this is a stupid question but

I’m 21 years old UK , I had £40,000 saved in premium bonds for a while. I’ve now just put £20,000 into S&P 500 (acc).

I now have £20,000 left , I don’t intend on buying house for a few years. I’m comfortable and don’t live a lavish lifestyle. How can I grow, invest this other £20,000? Thanks in advance 🤝🏻