As described in the introduction of the section Tables in worksheets, the ribbon command Insert | Table allows you to create "Tables in Worksheets". Below you will learn how to remove such a table.
There are two options for this:
A) Converting a table back to a normal cell range
To convert a table back to an "ordinary" cell range, move the cell frame to any cell within the table.
Then choose the command Convert to range 
on the contextual ribbon tab Table | group Table. (Alternatively via the context menu by right-clicking in the table)
In the following dialog box, click on the checkbox Remove all formatting from the cells.
This will remove the "magic" of the table features from all cells that were part of the table – including the automatic formatting and the AutoFilter.
B) Deleting a table with its entire content
To completely delete a table including all its contents, move the cell frame to any cell within the table.
Then choose the command Delete table 
on the contextual ribbon tab Table | group Table. (Alternatively via the context menu by right-clicking in the table)
This will delete the entire table, including the content of all cells that were part of it.