installing templates on joomla 3 site

Hello there , currently i have like only basic level of knowledge on joomla from watching youtube videos. I managed to install a template 2 weeks ago into the site however from last week till now, it keeps on giving this error message when installing templates, i tried to install from URL, upload package file and still doesnt work. I only have a superuser account but not sure who is the website host because its a website created in 2002 i think, im also unable to update these updates shown on the joomla site. Please help it feels like im stuck and going in loops, unable to resolve anything for the past 1 week