The reason supermarkets tell you to keep the plastic bag in place is so the plant won't collapse - many of them collapse outwards when the support of the bag is removed. I always remove them anyway, just in stages, moving it downwards over time if the collapse thing is likely to happen.
The pot's too small and its run out of root room - put it in a larger pot with some decent potting soil, water well. I'd trim off the tops, back down to where you can see smaller, healthy leaves, cutting just above those - hopefully you can make use of the leaves you've removed, well, at least the ones which are healthy.
Because its not got enough room for its roots, that makes it difficult for the plant to get enough water, even if you water daily - there's not enough soil in the pot to hold onto water. You may find you don't need to water daily in a larger pot, but check by feeling the top of the compost with your finger - if it feels dry to touch, water, but don't wait till the soil's shrunken from the sides of the pot. You can also just pick it up - you can usually tell by the weight whether it needs water or not. When you do water, water well, but don't leave it standing in any outer container full of water - empty that after half an hour. And water from the top, onto the soil in the pot, regardless of the supermarket instructions.
If you're keeping it indoors, find a bright spot for it, not full sun, some sun is beneficial evening/morning, but just bright daylight will be fine.