Back up issues windows 10 ?norton 360

Hello, thanks for reading, help sought, but I must advise that many terms and abbreviations just confuse me.

Over years I have backed up using Windows 7 back up and previously Vista etc. which all form part of my current, (C) drive data.

I now use win 10, which I find intrusive like a controlling partner, but the deed is done so have to accept that it does not let me choose the options I want in terms of data and alternative drives on backing up.

Having been advised, I started running  a System Image with my back ups, once I changed to win 10, and whenever I added/uninstalled applications.  In my ignorance, I was doing this in addition to regular ' File back ups' (question: is file b/u the same as 'history file b/u')?. 

. Somehow,  I now have only 40GB of space left on my 'Main', 'Local'  '(C)' Drive hard drive, which is 500GB.

Further complication comes in when I followed a prompt to enable the b/u facility of my Norton 360, which I now run on auto, but I noticed  that it was recording last b/u dates and times on my win control panel b/u page, so thought it has merged and worked 'as one', Oh dear, in addition to the Norton auto,  I have run b/u and system image from the control panel page when a m/s prompt has said to back up.

I now believe that this is the cause of my bloated file and that I have doubled and trebled up on files, but as the files are just series of numbers when I explore the (C) drive, I cannot identify, isolate and remove duplications.

I would like to stop using my Norton back up if I could, BUT, win 10 b/u will only permit one external back up option, even if I remove one drive and try another, ( it just won't recognise the latter). The idea being to run a new clean, b/u onto a borrowed drive, then delete, my b/u drive, re-connect it and hopefully by just running 'System Image, just have one image which would include all my applications, and libraries, once only, before deleting and returning borrowed drive.

Does it make sense?

Regards ( be kind to me I am old and the brain is atrophying fast. Ha-ha.