In a ranch house with sizeable but undeveloped attic space, you can create usable space by adding dormers. They can be shed dormers (a single flat roof at a flatter angle than the main roof), or gable dormers (with a peak that runs perpendicular to the main roof peak).
Shed dormers tend to be less expensive to have built, but gable dormers usually look better, particularly on the front of a house. An important consideration, if you are creating living space in the former attic, is where to put the stairway. This may be a problem for your first floor plan, if the house was originally built without a stairway.
A more extensive alternative to a dormer is taking the roof off and adding a second story. This is obviously a major renovation, and you will probably want to live somewhere else while it is being done. It will double the usable floor space in whatever part of the house you add the second story. You should make careful plans and perspective drawings before an addition of this kind. Planned properly, it can greatly improve the look of the house, as well as expanding its interior. Planned poorly, it can make the house look awkward, overblown, and out of proportion.
Footprint extensions are additions that actually increase the size of your house on the ground, and require new foundation work. This kind of renovation and extension is substantially more expensive than dormers or added stories, due primarily to the excavation and foundation work. However, adding more square footage to the ground floor is also more useful in the long run. Careful calculations regarding the cost of the addition and how much it is likely to add to the resale value of your home, will give you an idea of the feasibility of the project.