If you wish to change the look of your Shop Front header, you will be able to do this in your Shop Editor by editing your current header content block or adding a new content block.
Select Content > Headers and you will get a list of different header options.
If, for example, you do not wish to have a search bar in your header, you can select one of the header options without a search bar. Examples shown below.
If you want to make any edits to your header content block (adding background image, changing buttons, adding padding etc), you can hover over the right hand side of the content block and select the 'cog' symbol when it appears.