To modify the theme on Blogger (also known as Blogspot), follow these steps:
1. Sign in to your Blogger account and navigate to the dashboard for your blog.
2. In the left menu, click on the "Themes" option. This will open the theme editor, where you can customize the look and feel of your blog.
3. To change the overall theme, click on the "Customize" button in the top right corner of the theme editor. This will open the theme customization menu, where you can choose from a variety of pre-designed themes, or create your own custom theme.
4. To change specific elements of your theme, such as the font, colors, or layout, use the options in the left menu of the theme customization menu. For example, you can click on "Fonts" to choose a different font for your blog, or click on "Layout" to adjust the layout of your blog's pages.
5. As you make changes to your theme, you can preview them in real-time by clicking on the "Preview" button in the top right corner of the theme customization menu.
6. When you are happy with your changes, click on the "Apply to Blog" button to save your changes and apply the new theme to your blog.
Note that modifying the theme on your blog will not affect your existing blog posts or pages. However, it may change the way they are displayed, depending on the specific changes you make to your theme. It is always a good idea to preview your changes before applying them to your blog to ensure that they will look as you expect.