Change default order posts in search results page

Hello Richard,
Try the below code under Theme Setup >General Setup >Custom css

ul.orderby li:first-child {
display:none;
}
ul.orderby li:nth-child(1) {
display:none;
}
ul.orderby li:nth-child(2) {
display:none;
}
ul.orderby li:nth-child(3) {
display:none;
}
ul.orderby li:nth-child(7) {
display:none;
}