next year i'm going to

In my greenhouse I got this tomato blite on part of the first tomato plant as I left the door open.
So next year I was going to grow melons in there but was wondering about the soil in the border.
Do you think I should change it or just put a compost on top?

I'd change it if you got blight in there, personally, even if you don't intend to grow tomatoes as I've heard that it can stay in the soil for a few years  

Hope this helps
Su

Blight does not remain in the soil only on the plant/leaves/fruit which you should burn or dispose of and not compost