At the time of making a redesign of a subject or it soles WordPress most of the changes are realised on the style sheets, that is archives CSS.
A good form to make changes of style is to create a new style sheet and to include it in header.php directly. Assure to you that the line that your CSS loads is the last one of all, must not have no other declaration of CSS after yours. This way you will be able to sobrescribir any rule CSS that has been declared previously, not only of the subject but also of plugin or a slider. It is a very clean form to publish styles in a group or WordPress subject without modifying the existing files. Of this form if there is to update the subject you will be able to make it with the only exception conserve your leaf CSS and return to modify header.php since we have mentioned previously.