Depending on the cause of your cracks, there may be no sure fix. Houses expand and contract with changes in temp and humidity levels. drywall doesn't expand as much as the wood does and that means that something has to give. Viola, cracks in your walls. You could fix them, but they may be back to haunt you in the future.
In order to fix the cracks so that it isn't noticable, you'll need to use similar equipment to reapply the texture as was used in the first place. I suspect that a "Hopper Gun" was used, spraying a thinned joint compound over the surface, then knocking the texture down with a large taping knife. You can probably rent the gun and the compressor to drive it, but I'd suggest that you have a surface to practice on before you attempt to try this in your home.
To fix the crack, I sand down the texture first, then I use border adhesive to glue "paper joint tape" over the cracks. Then I use successive THIN coats of joint compound to "Feather" off the tape. Sanding the patch to keep it from being too visable under the texture as well as to feather the edge of the knockdown. Prime the patch with a quality latex primer to give yourself some extra working time, then spray the joint compound over teh patch and knock it down with a 10" taping knife. When it's dry reprime and repaint the wall.