Good lord, that Bob Martin stuff should be banned, it doesn't work and can kill cats. Probably why his eye is swollen.
Don't buy anything from pet shops or supermarkets. Ever.
Because he is a kitten, I would only be buying flea treatments from the vet at the moment.
If you want to save money when he's an adult, you can buy Advantage online (after ensuring the EXACT weight of your cat), but he's a kitten, so will be nowhere near the minimum weight (4kg) for Advantage. He's probably around 1.5 - 2kg at the moment, so flea and worming should be overseen by a vet, to avoid poisoning your kitten.
I agree with Polter about the deep bath, and towels lining the bottom of the bath. Ensure he's rinsed very well. Then wrap him up in a nice warm fluffy towel, and stroke him dry with it, if that makes sense?
You might want to invest in a flea comb for afterwards, have a cup of hot water close by, to drown them in if you spot any on the comb, which works best when wet. Be v. gentle though, he may be sore from scratching flea bites. Avoid the tummy button area, about half way up their lower body.