There are times when you need to update existing web part on your SharePoint site. SharePoint Object model and SharePoint WebServices can be used to accomplish that.

First, you can use SharePoint Object Model API in order to update a web part. Below is an example in C# how it can be achieved.

using (SPSite spSiteTest = new SPSite(“SharePointSiteURL”)
{
  using (SPWeb spWebTest = spSiteTest.OpenWeb())
  {
    SPWebPartCollection webparts = spWebTest.GetWebPartCollection("WebPartCollection", Storage.Shared);
   
    for (int i = 0; i < webparts.Count; i++)
    {
      //Get reference
      WebPart wp = webparts[k];
 
      //Check for Title Change
      if (wp.Title == "Web Part Title")
      {
        //Set New Title
        wpNew.Title = "Updated Web Part Title";
 
        //Save Web Part
        webparts.SaveChanges(wp.StorageKey);
 
         //Update Object
         spWebTest.Update();
       }
     }
   }
 }
Second way of updating SharePoint WebPart properties is via SharePoint Web service called "WebPartPages.asmx"
static void Main(string[] args)
        {
            WebPartPagesWebServiceSoapClient myWebPArtPages = new WebPartPagesWebServiceSoapClient();
            myWebPArtPages = Connect3("http://sharepoint/site/_vti_bin/WebPartPages.asmx");
        
           string pageUrl = "http:// http://sharepoint/site/pages/page.aspx";
           //Set text variable;
           string webPartText;
          
           Guid storageKey = new Guid("eerre74f-733c-4fd3-9fsb-4ea9fsae13903");
           webPartText = myWebPArtPages.GetWebPart(pageUrl, storageKey, Storage.Shared);
 
            //Build a string
           StringBuilder sb = new StringBuilder(webPartText);
 
           sb.Replace("Title", "New Title");
 
           // Call SaveWebPart to update the contents of the Web Part XML.
           myWebPArtPages.SaveWebPart(pageUrl, storageKey, sb.ToString(), Storage.Shared);
          
        }