If your ID field is a number you need to remove the string delimiters from it - try;
Code:
WHERE [ID] = " & Me.UserLogin
If not build the string before and examine it ;
Code:
Dim sSql as String
sSql = "Update tblUser SET tblUser.UserPassword = '" & Replace(Me.Text4.Value, "'", "''") & "' WHERE [ID] = " & Me.UserLogin
Debug.Print sSql ' This will make the result of you string appear in the immediate window. You can cut and paste that into the query editor to highlight the error
CurrentDB.Execute sSql