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;

using CMS.CMSHelper;

...

        // 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);