In Salesforce Lightning, you now have the option of several different templates to use for your Page Layouts. Once you select a template, you can add, remove and move around the components on the page.
Navigate to a record for the page layout you would like to edit. For example, Account:
Click the gear button at the top right-hand side of the screen
Select "Edit Page"
Here you will see many areas of the page. Find the "Template" field on the right-hand panel and click "Change".
Highlight the different templates to get a preview of the layouts. In this example, we selected "Header and Two Equal Regions".
Here the wizard has made some suggestions as to how to map your old sections to your new sections. You can use the drop-downs to customize or leave suggestions.
You are now free to edit the components of your new Layout Template. You can see that, since we selected the "Header and Two Equal Regions" template, we now have 3 sections to customize. Select the Left Region.
As you select Regions in your template, the panel on the right will update and allow you to customize.
You can move, add and remove the tabs in this region. In this example, we delete the "Related" tab, by clicking the X next to it.
On the left panel, you can find additional components to click and drag to your layout.
In this example, we added the Related Lists component to the right region.
You can then drag and drop components around your page. In this example, we move the "Activities" component from the Right Region to the Left.
When you are happy with your layout, click Save.
You may be prompted to Activate your page. Click Activate.
(If you are not prompted with this screen, click Activate at the upper right-hand corner of your screen)
You will be prompted to set defaults for this layout. We recommend Assigning your new layout as the Org Default. You may also do this at the App, Record Type, and Profile levels by looking through the other tabs.
Click Close when done.
Your new template is saved. Click Back to exit setup and enjoy!