Webminstats uses the rrd (round robin database) tool (https://oss.oetiker.ch/rrdtool/) : the database size is fixed at init, so the number of records is also fixed. It is possible to add a new RRA to store long term data : https://stackoverflow.com/questions/30322964/how-can-i-add-rras-to-an-existing-rrd but webminstats will not be able to display this data without some big code changes.