It's not was easy as it was in The Sims 3 but it can be done. There may be a better way if there is I would love to know it also.
After making your sim place them on a empty lot like you was going to play them. Once in the game go to the Options Menu by clicking the three dots in the upper right corner and select Manage Worlds.
Once the map opens click the lot with your sim and there will be three options, choose the last on the three dots, says More when you hove over it.
In the window that opens select Transfer Sims Between Households at the bottom. It's the button with two arrows.
This will open a window with you household on the left and the others will be on the right. On the right select the tab for unplayed, then select the town with the household you want to move your sim to. This will bring up a list of households in that town.
Select the household you want to move your sim to then select your sim and click the arrow between them to move your sim to that household. Then click the check in the bottom right corner. YOu will be taken back to the manage household map where you can select where you moved your sim to and select play.
Note, If you didn't place your sim on a empty lot but a lot with a house, when you move your sim you will probably want to check Sell
furniture On the left where you sims was. Or all the furnitue from that house will be in your family inventory and the house you moved from will be empty.
I know it sounds like a lot but it only takes a minute to do.
