In Blender, the way you get rid of a window is to merge that window into another one. There is a trick to this, however; two windows to be merged have to have the exact same common dimension, so sometimes you need to split one window in two to be able to merge part of it with another. Looking at your illustration, you can merge the window you want to keep with the window immediately above it by clicking on the splitter widget in the upper right hand corner of the window you want to keep, and while holding the LMB down, moving the mouse so the cursor moves into the region of the window just above it. You should see an faint arrow appear in the upper window showing that that window is being removed. For the window just below the one you want to keep, which extends across the whole screen, use the splitter widget to divide this into three windows, one the exact width of the window you want to keep, the other two windows with the exact width of the windows above them. Using the same technique as above, merge the three windows above into the three windows below.
Clearing the other windows is just a matter of applying the same techniques: finding two windows with a common dimension and merging them together, and if there are not two windows with a common dimension, splitting a window and sizing the resultant bits so that one of them has a common dimension with another adjacent to it.
There is another way: save your file, quite Blender, and start a new Blender instance. Navigate to the "file > open", and in the file browser, find the file you saved. Then, in the extreme lower pane of the file browser window, find the "Open Blender file" pane, and if the box labeled "load UI" is checked, uncheck it. This will load the contents, without loading the window layout.