carto - How to add rows from a Dataset to another?

The DB I have is divided in many datasets (shape format, each .zip I send to CartodDB consist of 4 files, .dbf, .prj, .shp, .shx). The problem is that the free account only allows 4 datasets, each one associated to a layer.

To solve this problem I'd like to join all my datasets in just one. All datasets share the same structure (same columns) due to the fact they form part of the same DB. I hope there is a way to add rows from one dataset to another.