Hi Amit,
I see several errors in this code:
1) user.SetValue(CurrentUser.FirstName, "")
the first parameter in this method is a column (property) name of UserInfo class, it can't be CurrentUser.FirstName
because, I think, it has dynamic value
2) user.SetValue
method with 2 parameters returns a boolean value which is a result of operation, you can't assign it to string property of textbox field FirstNameValue.Text
and you can't compile this code.
3) CurrentUser = MembershipContext.AuthenticatedUser, so there isn't any difference between them
The code should be like:
UserInfo user = UserInfoProvider.GetUserInfo(MembershipContext.AuthenticatedUser.UserName);
if (user == null) return; //check if user exists, if not, maybe you need to create him
user.FirstName = value; // or user.SetValue("FirstName", value)
UserInfoProvider.SetUserInfo(user); // or user.Update() if you know that user exists
FirstNameValue.Text = value;
Please, read Kentico documentation and look at Kentico Api references and read about C# programming, because it may help you to save your time)