Make my website perform better

I have two websites africanoverlanders.com and discoverafrica4x4.com, that I am happy with the design and they work, but they suddenly stop working. The website hosting company is telling me that the sites are underperforming and when the sites get used a lot they stop working with a 500 internal server error.

https://gtmetrix.com/reports/africanoverlanders.com/CXeYCApr/

I need someone to make both sites perform better so this doesn't happen at all. They also suggested using a VPS, that could help the situation.

https://www.uk2.net/vps-hosting/

I am open for this idea if it will help.

Thanks for your help