using CMS.Community;

...

        // Get group object by GroupID

      GroupInfo gi = GroupInfoProvider.GetGroupInfo(1);

      // Change group display name

       gi.GroupDisplayName = gi.GroupDisplayName + "_Updated";

      // Save object

      GroupInfoProvider.SetGroupInfo(gi);

using System;

using CMS.Community;

using CMS.SiteProvider;

using CMS.UIControls;

...

        // Create empty group object

      GroupInfo gi = new GroupInfo();

      // Set properties

       gi.GroupDisplayName = "New group";

       gi.GroupName = "NewGroup";

       gi.GroupSiteID = 2;

       gi.GroupDescription = "";

       gi.GroupApproveMembers = GroupApproveMembersEnum.AnyoneCanJoin;

       gi.GroupAccess = SecurityAccessEnum.AllUsers;

       gi.GroupApproved = true;

       gi.GroupApprovedByUserID = CurrentUser.UserID;

       gi.GroupCreatedByUserID = CurrentUser.UserID;

       gi.AllowCreate = SecurityAccessEnum.GroupMembers;

       gi.AllowDelete = SecurityAccessEnum.GroupMembers;

       gi.AllowModify = SecurityAccessEnum.GroupMembers;

       gi.GroupNodeGUID = Guid.Empty;

      // Save object to database

      GroupInfoProvider.SetGroupInfo(gi);