As described in the introduction of the section Tables in worksheets, the ribbon command Insert | Table enables you to create "tables in worksheets". Here, you will learn how to remove such tables:
In this case, you have the following options:
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, use the context menu by right-clicking in the table.)
In the following dialog box, select the checkbox Remove all formatting from the cells.
This will remove the "magic" of the table feature from all cells that were part of the table – including the automatic formatting and the AutoFilter.
B) Deleting a table and its entire content
To completely delete a table and 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, use the context menu by right-clicking in the table.)
This will delete the entire table – including all cell contents.