SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-forum-statistics

ForumStatistics_UpdateForumStatistics.cs

using System;
using Telerik.Sitefinity.Forums;

namespace SitefinityWebApp
{
    public class ForumStatistics_UpdateForumStatistics
    {
        public void UpdateForumStatuistics(Guid forumId)
        {
            ForumsManager forumManager = ForumsManager.GetManager();

            forumManager.UpdateForumStatistics(forumId);

            forumManager.SaveChanges();
        }

        public void UpdateThreadStatuistics(Guid threadId)
        {
            ForumsManager forumManager = ForumsManager.GetManager();

            forumManager.UpdateThreadStatistics(threadId);

            forumManager.SaveChanges();
        }
    }
}