Hi,
1. You can remove it by adding such CSS on your website:
.hikashop_filter__1 br{ display: none; }
2. It's because of either the custom CSS you added or the CSS of your template. Normally the colon is on the same line as the filter name. We would need to analyze the CSS on the page to tell you what to do.
3. Where do you do that ? Normally, you should do that in the "products options" tab of your menu item.
If you do it in the HikaShop configuration or in another menu item, it won't do anything.