To change the website title, please take following steps:
In the Joomla administration panel, go to Menus >>Main Menu
Next, in Menu Item Manager page, select item, example: Home
Next, Menu Item page, open section Page Display Options and change parameter Browser Page Title as you desire.
Remember that page title is an important part for your search engine display. It should be less than 70 characters to be more effective to increase clicks to your site from search result
You can do similar steps with article SEO parameters.
Another way to set SEO parameter for your page is choose Component Heading and Content Heading in Template Managers. The importance of content is devalued from H1 to others. Please check out our Template Setting to know more.
You can also customize values of header tags of modules in the advanced setting section of those modules.