There are plenty of resources online that cover this topic, and they are potentially better written & illustrated, however, this is a short explanation of the typical process I follow, & the various steps involved.
Firstly, I’m assuming you have some ideas around what it is you’d like refreshed; this is generally a selection of websites you admire visually, or, that have functionality currently missing from your site. Once I have these details, I can then create what’s called a staging website. A staging website is an exact duplicate of your existing site that I can work on to incorporate design & functionality changes – without having any effect on your live site.
I’ll need administrator-level login details to your live site, to create a staging site
What I will need from you at this point is either, access to your domain name, or, I can provide you with the details (an a-record) that will need to be added – for you to be able to view/access the staging website.
I’ll keep the staging website behind a holding page, so only people you choose can view it (while we work on it). Once the staging website is complete, it’s merely a matter of migrating from staging to live. At this point, the a-record added above can be removed.
Requirements – admin login details to your live website + login details to your domain name, or, the ability to add an a-record (that I will provide) yourself.