Download the installable WordPress file dt-the7-x.zip (fig. 1):
Go to “Appearance > Themes > Add New > Upload Theme > Browse” (see fig. 2) and choose the theme installation file:
If any warnings appear, most probably, your hosting has file size limit. In this case, you can ask hosting support to increase the limit or install theme via FTP. Simply unzip dt-the7-x.zip and upload the theme folder via FTP into “/wp-content/themes/”. So that the theme is stored in “/wp-content/themes/dt-the7/”.
In “Appearance > Themes” activate the Theme by hitting the correspondent “Activate” link.