Vertical blinds are much easier to remove than they are to install. There are no measurements to take, no marks to make on the wall, no leveling, no nonsense. But the screws that hold the hanging brackets to the wall will leave scarring, and those holes and other imperfections should be fixed before you call the job finished. You must do a little touch-up painting, and there will also be a small amount of dry time. So plan on this project taking a little labor time spread across a couple of days.
Slide the vertical blind louvers closed so they are separated and the louver clips are accessible. The louvers themselves should be open, so you can see out of the window.
Slip a credit card, or something similar, between the louver and the louver clip at the top end of the louver. Swing the bottom of the louvers away from the window, and pull them out of the louver clip. Repeat for each louver.
Place a flat screwdriver between the headrail and the release clip on the headrail bracket. Turn the bottom of the headrail away from the window to remove that headrail from the bracket.
Remove the screws that hold the brackets to the wall with a drill and the appropriate drill bit style (either flat or phillips).
Fill the holes in the wall left by the screws with spackling compound or drywall joint compound. Spread the spackle or joint compound with a putty knife. Allow the compound to dry, and wipe the excess compound off the wall with a damp rag or sponge.
Touch up the spackled holes with paint that matches the wall.