I had to ask as it's unusual to see 3 cards on a phone, I would be interested how they break that down, there would only be 1 physically removable card I'd imagine, so it's figuring out if it's the OS breaking it down this way, or if it's the way the makers have gone about making the phone, if you wanted to find out the easiest way is probably remove the card, then see what the PC shows without a card in there.
I can only think of 2 possibles, they are either using flash memory (as you would add a card), and have included a storage area built into it, so the phone + mass memory + memory card, OR, the memory card has been broken down into 2 elements, looking at the manual it talks about using it as mass memory, and as such is not accessible by the phone directly if I recall, so it could be the phone + memory card + mass storage on the memory card.
Clearing the browser, or anything on the phone via the phones\applications menu's is perfectly safe, and the way to do it, I was warning about going in via the PC and removing such files, as you would have no idea what effect it could have on the phone, and if you deleted the wrong files\folder, you could end up messing up the phone, but via the phone if it's an option then thats the only way to do it safely.