Determine a model for forecasting

Hi, We're working on a project for simulating and forecasting sales and profits for a company. I've seen MATLAB has many inbuilt models like ARIMA and GARCH. The excel file for sales has been provided. Seeing the values,please suggest whether we should use an ARIMA model or the GARCH model would be better.

I've seen this example: http://www.mathworks.in/help/econ/forecast-airline-passenger-counts.html 
But is this model only applicable to increasing values only?

Any other link or examples would be of great help. Thanks a lot.