Non technicrat needs advise.

I have Acronis on my computer and an external hard drive which is one terabyte in size. I am so technically incompetent that I don’t know how to check what type of Acronis I have. When I looked at it by clicking onto “My Computer” it shows just 2.62 Gigabyte free which presents me with a number of questions.
1. I thought that Acronis did a rolling back up where it replaced the existing backup with a new one so what happened and what should I do?
2. I initially assumed that I should dump everything on the external hard drive and start again. However, when I looked at the content of the external hard drive some of it is quite old and last week when I was unable to find a folder of quite old photographs I eventually found them on the external hard drive. I have no idea how I lost them from the computer but there it is but I don’t want to lose any of the old stuff.
3. I keep receiving E-Mails trying to sell me an upgrade. What is to be gained from upgrading?