The tried and true (and cheapest) method is just to wait it out. The redness (not bumpiness) is called "hyperpigmentation" which basically means the skin coloration is darker than normal. Time eventually lets your skin to heal and they'll fade away. Unfortunately, the time method is also the slowest method there is. Just make sure you're doing things to prevent any additional acne, and your skin just eventually heals up.
Since there's no physical bumps, concealer and foundation usually do a good enough job of hiding the redness until your skin heals.
It takes usually around 6-12 months for my redness to go down to a level where I don't need concealer anymore, and another 6-12 months on top of that where they'll finally just lighten up until they fade away. I think that I heal slower than normal though, since from what I've read, most people are back to complete "normal" again in 3-6 months, whereas for me that much healing takes well over a year. (It's been about 12 months since I had my last pimple, and I've finally gotten to a point a few weeks ago where a quick application of my EDM pressed powder will even out my skin to make the spots unnoticeable.) If I ever get a spider bite that turns dark purple (3-4 months), it then turns dark brown (3-4 months), then light brown (3-4 months), then fades away. Those spots also take around a year to go away on me.
Some of the prescription drugs out there worry me because it can actually cause like bleaching spots on your skin (it lightens up the red spots, but it also lightens up your normal skin) so you end up getting like...halos around your spots. So I'd recommend seeing a dermatologist if you're looking into any of the stronger stuff.
/emoticons/
