First step is a health check up. Often a big behavior change like this is due to a health issue and in cats urinary tract infection, bladder stones or crystals are common problems.
If it is not a health issue then you might try Feliway cat appeasing pheromone which you can read about here
http://placervillevet.com/feliway.htm
Clean any marked spots with an enzyme based cleaner to eliminate the odor. Odor Mute, Simple Solution, and Nature's Miracle are typical cleaners used that work well as the enzymes digest the urine and break it up into odorless components.
Hope this helps you!
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