Hi,
If you look at the HTML of the dashboard with your browser inspector (like the CSS tutorial Jerome gave you), you can easily know the id that you need to use in your CSS to hide the areas you want:
monosnap.com/file/ZKgE58Jt7hB3tTtkJfZK8Sp4XLMLl3
So for example here, if you want to hider the total orders block, you can add such CSS:
#hikashop_dashboard_stat_sales_count{ display:none; }
Since it is in the backend of HikaShop, you want to add that CSS in the backend CSS file of HikaShop under the Display tab of the HikaShop configuration.