Reflection to simplify this?

I have third party dll (which I cannot modify). It has properties like...
Class1.Usernumber1
Class1.Usernumber2
Class1.Usernumber3
Class1.Usernumber4
Class1.Usernumber5

Now, in my code (which I can modify) I have a variable "i" which can be 1-5. Based on its value I need to use the corresponding property. So, my current code looks something like
if (i == 1)
    Class1.Usernumber1 = x;
else if (i == 2)
    Class1.Usernumber2 = x;
else if (i == 3)
    Class1.Usernumber3 = x;
else if (i == 4)
    Class1.Usernumber4 = x;
else if (i == 5)
    Class1.Usernumber5 = x;

Is there reflection o ...