I followed the these instruction below:
Now click on Install From Web tab in Extensions: Install section.
Search for Sellacious in the search box. After search results appear, click on the first one i.e. Sellacious.

It started to install then i followed this step:
Click on Download & Install Now button to install the Sellacious additional libraries, but no Download & Install Now button is showing, i re installed joomla 3 times and 3 times same thing, no Download & Install Now button, i can see under Components Sellacious and when i click on it the same page comes up as per attachment.

Please can someone help me with this issue?
Sorry if i am not explaining it properly but i am a nooby with Joomla.

Thank you in advance.