According to Steam support, it is not possible for a user to delete or merge a Steam account. It is also impossible to modify an individual Steam ID or Steam account name. But Steam can be removed from a computer using Windows.
- Exit Steam
Right click the Steam icon in the lower left hand corner of the taskbar and select exit.
- Select control panel through the Windows start button
Once the control panel is opened, click on programs and features to browse through a list of installed programs. Once Steam is located, right click and select uninstall.
- Select yes when prompted to uninstall
The removal of Steam will take place automatically. Once this process is completed, Steam and any other globally-installed games are removed from the user's computer.