The first step is to login to your account (you should know this by now from the above notes).
I gather that you did save your work as a layout so thats done too. If unsure go back to the previous notes above to refresh.
Now that you have a saved layout its time to find where it lives.
Click on My Account once you login. You will be taken to Your Profile page.
To the left you will see a number of tabs. Two we will focus on here. These are:
Click on Saved Layouts. You will see your layouts listed on the next page. Click on EDIT to the right of the Saved Layout.
The layout will open in the designer mode. Here you can now do any editing if you require. Once happy proceed to check out.
In case you want to add a second layout just click the big CLOSE or "X" to the top right corner of the page and it will take you to the website. Next click on My Account, then click Saved Layouts to access layouts again. Follow the same process as above and once ready click BUY to check out.
Everything is explained in detail in the video below.