On your dashboard go to appearance > Customize > Header > Site Title & Logo. From Site Identity, you will be able to add various options related to site identity like:
- Logo( Only available in WordPress version greater than or equal to 4.5 ): It changes the main logo of the site.
- Site Title: It changes the main site title of the site.
- Tagline: It changes the tagline (i.e:Description) of the site.Just below site title.
- Display Site Title and Tagline: This enables/disables the site title and tagline from the site.