Change the default tile size/tumbnails view in image library in Sharepoint 2013

Using a CSS only approach, add the following CSS inside the content editor webpart or add it to your custom css.

<style type="text/css">
            div.ms-promlink-body {
                height: 130px;
            }
            div.ms-tileview-tile-root {
                height: 150px !important;
                width: 150px !important;
            }
            div.ms-tileview-tile-content, div.ms-tileview-tile-detailsBox,  div.ms-tileview-tile-content > a > div > span {
                height: 140px !important;
                width: 140px !important;
            }
            div.ms-tileview-tile-content > a > div > img {
                max-width: 100%;
                width: 100% !important;
            }

            ul.ms-tileview-tile-detailsListMedium {
                height: 100px;
                padding: 0;
            }
            li.ms-tileview-tile-descriptionMedium {
                font-size: 11px;
                line-height: 16px;
            }
            div.ms-tileview-tile-titleTextMediumExpanded, div.ms-tileview-tile-titleTextLargeCollapsed, div.ms-tileview-tile-titleTextLargeExpanded {
                padding: 3px;
            }
             div.ms-tileview-tile-titleTextMediumCollapsed {
                font-size: 12px; !important;
                padding-left: 6px; !important;
            }
             li.ms-tileview-tile-descriptionMedium {
                font-size: 11px;
                line-height: 14px;
                padding: 3px;
            }
           
</style>