How can I access the Cloud on my Kindle Fire please anybody?

Every Kindle book you ever buy is stored in your Amazon account in the Cloud.  You can delete all the books from your Kindle or your tablet, whether you've read them or not, and they'll still be in your account available for download whenever you want them.  Deleting books from one device doesn't delete them from the other device.  And if you want to download deleted books to either your Fire or your Kindle again at any stage, all you have to do to get them back is this:

Under Your Account, go to Manage your content and devices
Find the book you want to download
Click on the little Actions box to the left of the book title
Then you can choose to Deliver To whichever device you want to read it on, if you want to send it via wifi, or Download via USB if you want to transfer from a PC. 

Alternatively, if you want to download a book to your Fire, go to the Kindle Library on your Fire, as this will continue to show all the titles you've bought, even if they haven't been downloaded to the Fire, so you can always scroll through everything you've bought to find what you want to read.  Then you just need to click on the title to download it.  (I'm assuming here that, since it's a tablet, the Fire works in this respect exactly as the ipad Kindle app does...  Would be a bit daft if it didn't, but if not see my instructions above).

By the way, as well as deleting books from your device to free up space, you probably also want to turn off the automatic download feature so that new purchases stay in the cloud until you want them.  I THINK the only way of doing this is to make another device your default download device (again, via the Manage your content and devices page), but you can make this your Kindle or PC or wherever you've got more space.

If any of that isn't clear, Sal, do let me know.

This would annoy me too, so I always delete books from my Kindle as soon as I've read them.