If your blade isn't sharp enough to cut through items like a carrot or apple then you have some very dull knives. Don't worry, they can still be sharpened; you just need proper tools and the right amount of patience. One way to sharpen up such dull blades is by using a table grinder (such as those seen in factories). It might seem a bit excessive, but this method works quite well – it will grind down any jagged edges of your blade so that it's smooth again.
Another option that'll work for even the bluntest of knives is getting an electrical file and slowly filing away at your edges until they're both smooth and pointed. Always be sure to file away from your hand so that you don't accidentally cut yourself.
In either case, make sure to follow any instructions listed on the package that comes with any of these tools before using them.