If you're using the Yoast SEO plugin (which it looks like you are) then [this](http://wordpress.stackexchange.com/a/163023/96768) answer might help you


> If you are using yoast SEO plugin then the easiest method is to remove
> the archive word from "titles & metas-> Taxonomies->category"
> 
> find:
> 
> %%term_title%% Archives %%page%% %%sep%% %%sitename%% replace it with:
> 
> %%term_title%% %%page%% %%sep%% %%sitename%%

Alternatively you could try changing it using the `get_the_archive_title` filter as explained [here](http://wordpress.stackexchange.com/a/179590/96768)

> 
>     add_filter( 'get_the_archive_title', function ($title) {
> 
>     if ( is_category() ) {
> 
>             $title = single_cat_title( '', false );
> 
>         } elseif ( is_tag() ) {
> 
>             $title = single_tag_title( '', false );
> 
>         } elseif ( is_author() ) {
> 
>             $title = '<span class="vcard">' . get_the_author() . '</span>' ;
> 
>         }
> 
>     return $title;
> 
>     });