How do i convert 2 story house to 1 story?

One way to do it might be to save the bedrooms to the gallery individually, delete the second floor of your lot, and then download the bedrooms again and place them where you want on the first floor. I haven't done it myself, though, so I'm not entirely sure on the process or if there's any little fiddly tricks that might make it easier.

If you have the space for it you could try this. First demolish the roof. On your top story remove all the doors by clicking them with the sledgehammer so that it removes the piece of wall too. Now save your whole top story as one big room to your library. Because of the wall gaps it should work. Go to your library and place down that room. Once it and all your furniture is placed safely next to your existing bottom story then go back upstairs and click the top room and hit delete. Now build a roof over your whole one story house ;) Dont forget to add the piece of wall and doors back in your moved rooms :)

You don’t need to save the top floor to the gallery. Once you delete a wall from all rooms as suggested above, you can click the ‘room’ and there should be an option to move it entirely. From there you can just lower it to the downstairs

Just click on the room and then the "move" arrows. Once you are "carrying" the room with the arrows, you can click on the "down" button at top right to bring up the lower floor, and simply place each room where you want it on the lower floor.

You can do the same thing with the roofs afterward.

I suggested the above method because some simmers are experiencing issues with furniture staying in place or some of it not moving with a room or even when trying to move a whole house. I had it happen trying to move one room to the other side of a house.

"mcrudd;c-18295913" wrote:
I suggested the above method because some simmers are experiencing issues with furniture staying in place or some of it not moving with a room or even when trying to move a whole house. I had it happen trying to move one room to the other side of a house.

i agree yes im getting that glitch also when i try to move my house on lot furniture and floor tiles move too :(

i reported it to Answers Hq on the forum

"mightysprite;c-18296612" wrote:
Oh thanks @mcrudd , didn't realize that was a potential issue.

Yeah it is pretty strange how some bugs only affect some players even if they are both for instance playing Vanilla. I just thought I would add that way because I read of that bug in some posts and experienced it with a room I tried moving. I also have little thought bubbles popping up everywhere. My sim would be in home and I would see one, I once paused the game to track it down and it was so far away from my sim's house, way out in the world and it was a sim eating at a park bench thinking of something. So weird, I just ignore them for now, but have not seen anyone mention the same bug anywhere so far anyways LOL. I try to not mention bugs because the threads get closed and we get told to go to HQ Help forums. So we are not always aware of potential issues when advising others unless we experienced them or saw a thread before it got locked ;)

Oh thanks @mcrudd , didn't realize that was a potential issue.