Static HTML Website Content Refresh

Small content updates to an existing static HTML website (no redesign)

I have an old, simple static HTML website hosted on a cPanel account with WebWorld (an Irish host). The site works well and ranks well on Google. I do NOT want a redesign, rebuild, migration, or change of host.

The job:

Locate the live site files on the hosting account. cPanel access will be provided.
Take a full backup of the site files before making any changes, and supply me with a copy.
Update text on approximately 10 pages — new wording will be supplied.
Replace approximately 35-40 images — new images will be supplied.
Fix up the banner photos and the side navigation bar.
Optional (quote separately): enable HTTPS. The site currently only works on HTTP. Enable AutoSSL/Let's Encrypt in cPanel and fix any hardcoded http:// links so the site loads cleanly on https, with a redirect from http.
Add in a viewing panel from an Instagram account.
Strict requirements:

No changes to page filenames, URLs, site structure, or navigation
No changes to page titles or headings unless included in the supplied text
No frameworks, builders, or CMS to be introduced — plain HTML edits only
Hosting stays with WebWorld — no migration
Google rankings must not be disturbed
Access provided: cPanel login (File Manager and FTP available).