How do I capitalize first letter of first name and last name in C#?

CultureInfo.CurrentCulture.TextInfo.ToTitleCase("hello world");

String test = "HELLO HOW ARE YOU";
string s = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(test);

The above code wont work .....

so put the below code by convert to lower then apply the function

String test = "HELLO HOW ARE YOU";
string s = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(test.ToLower());

TextInfo.ToTitleCase() capitalizes the first character in each token of a string.
If there is no need to maintain Acronym Uppercasing, then you should include ToLower().

string s = "JOHN DOE";
s = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(s.ToLower());
// Produces "John Doe"

If CurrentCulture is unavailable, use:

string s = "JOHN DOE";
s = new System.Globalization.CultureInfo("en-US", false).TextInfo.ToTitleCase(s.ToLower());

See the MSDN Link for a detailed description.