Once you have logged in to your website and you are now located in the dashboard you can now update the content on any of your pages of your website (pages are different to blog posts)
Click on the pages tab as shown below. This should bring up a list of the pages that are on your site.
see below sample from my website:
click on the TITLE of the page you wish to update and this will then open that page for you.
For this example I will click on the About page in my list.
Once the page you want to update opens, edit any of the wording/images that you wish to change and then click update on the right hand side as circled. This has now been updated live on your website!
as always, you can find as much info as you want to know about your wordpress site over here.