code:

DWORD UpdateAccountPassword(
        LPTSTR szServerDNS,   // DNS name of host computer
        LPTSTR szAccountDN,   // Distinguished name of service logon account
        LPTSTR szServiceName, // Name of the service
        LPTSTR szOldPassword, // Old password
        LPTSTR szNewPassword  // New password
        )
{
SC_HANDLE schService = NULL;
SC_HANDLE schSCManager = NULL;
 
DWORD dwLen = MAX_PATH;
TCHAR szAccountPath[MAX_PATH];
IADsUser *pUser = NULL;
HRESULT hr;
 
DWORD dwStatus=0;
SC_LOCK sclLock = NULL; 

if(!szServerDNS || !szAccountDN || !szServiceName || !szOldPassword || 
   !szNewPassword)
{
    _tprintf(TEXT("Invalid parameter"));
       goto cleanup;
}
 
// Set the password on the account.
// Use the distinguished name to bind to the account object.
_tcsncpy(szAccountPath, TEXT("LDAP://"), MAX_PATH);
_tcscat(szAccountPath, szAccountDN, MAX_PATH - _tcslen(szAccountPath));
hr = ADsGetObject(szAccountPath, IID_IADsUser, (void**)&pUser);
if (FAILED(hr)) {
    _tprintf(TEXT("Get IADsUser failed - 0x%x\n"), dwStatus = hr);
       goto cleanup;
}
 
// Set the password on the account. 
hr = pUser->ChangePassword(CComBSTR(szOldPassword), CComBSTR(szNewPassword));
if (FAILED(hr)) {
    _tprintf(TEXT("ChangePassword failed - 0x%x\n"), dwStatus = hr);
       goto cleanup;
}
 
// Update the account and password in the SCM database.
// Open the Service Control Manager on the specified computer.
schSCManager = OpenSCManager(
                szServerDNS,            // DNS name of host computer
                NULL,                   // database (NULL == default)
                SC_MANAGER_ALL_ACCESS   // access required
                        );
if (! schSCManager) {
    _tprintf(TEXT("OpenSCManager failed - %d\n"), dwStatus = GetLastError());
    goto cleanup;
}
 
// Open a handle to the service instance.
schService = OpenService(schSCManager, szServiceName, SERVICE_ALL_ACCESS);
if (! schService) {
    _tprintf(TEXT("OpenService failed - %s\n"), dwStatus = GetLastError());
    goto cleanup;
}
 
// Get the SCM database lock before changing the password. 
sclLock = LockServiceDatabase(schSCManager); 
if (sclLock == NULL) {
    _tprintf(TEXT("LockServiceDatabase failed - %d\n"), dwStatus = GetLastError());
    goto cleanup;
}
 
// Set the account and password that the service uses at startup.
if (! ChangeServiceConfig( 
        schService,        // Handle of service 
        SERVICE_NO_CHANGE, // Service type: no change 
        SERVICE_NO_CHANGE, // Change service start type 
        SERVICE_NO_CHANGE, // Error control: no change 
        NULL,              // Binary path: no change 
        NULL,              // Load order group: no change 
        NULL,              // Tag ID: no change 
        NULL,              // Dependencies: no change 
        NULL,              // Account name: no change 
        szNewPassword,     // New password 
        NULL) ) {          // Display name: no change
    _tprintf(TEXT("ChangeServiceConfig failed - %s\n"), dwStatus = GetLastError());
    goto cleanup;
}
_tprintf(TEXT("Password changed for service instance on: %s\n"), szServerDNS);
cleanup:
 
if (sclLock)
    UnlockServiceDatabase(sclLock); 
if (schService)
    CloseServiceHandle(schService);
if (schSCManager)
    CloseServiceHandle(schSCManager);
if (pUser)
    pUser->Release();
 
return dwStatus;
 
}

code:

using System;
using System.DirectoryServices;

namespace OLAActiveDirectory.Management
{
public interface IADPasswdManager
{
void ChangePassword(IADUser objUser,string strOldPasswd,string strNewPasswd);
void SetPassword(IADUser objUser,string strPasswd);
}
public class ADPasswdManager : IADPasswdManager
{
public ADPasswdManager()
{
}
public void SetPassword(IADUser objUser,string strPasswd)
{
DirectoryEntry objLoginEntry=objUser.DirectoryEntry;
if(objLoginEntry!=null)
{
objLoginEntry.Invoke("SetPassword", new object[]{strPasswd});
objLoginEntry.CommitChanges();
}
}
public void ChangePassword(IADUser objUser,string strOldPasswd, string strNewPasswd)
{
DirectoryEntry objLoginEntry=objUser.DirectoryEntry;
if(objLoginEntry!=null)
{
objLoginEntry.Invoke("ChangePassword",new object[]{strOldPasswd,strNewPasswd});
objLoginEntry.CommitChanges();
}
}
}
}