Problems with new sketchs!

First of all, i have to say that im new in the arduino world. I have an arduino uno and a little knowledge of programing. Also, i have to say that my english isnt very good because i talk spanish.

I have a question for those who really know about arduino. The question is that when i charge a new sketch to my arduino, the previous sketch is deleted? Because i tried to charge a new sketch to my arduino but it seems that the sketch that the arduino has on is the old one and not the new one.

I wish you have understanded me.

Thanks!

You are correct. If you succeed in uploading a new sketch to the arduino, the old one is deleted. But sometime/often, the upload is not successful, so the old sketch remains on the board.

Thank you for the reply jackwp. But those time that the upload is not succesfull, does the pc Arduino IDE program says something like an error or it only says succesful upload even the new sketch is not uploaded?

I have had it say both, even when it did not upload. Usually the message is correct tho.
One think I count on, is watching the led lights on the arduino. If the flicker a time or two, then 4 of them start flickering fast, I normally assume the upload was a success. Don't know why, but what is, is.

Fausto24:
Thank you for the reply jackwp. But those time that the upload is not succesfull, does the pc Arduino IDE program says something like an error or it only says succesful upload even the new sketch is not uploaded?

In preferences, turn on "verbose output". This will give more information.