What is the best way to download my family tree to a file in my computer?

I believe it is the only way. And believe it requires a program which can use it. Will be looking to see what programs folks suggest.

GEDCOM is an outdated, but still the only one, standard of exchanging genealogical event-data (i.e. births, marriages, deaths) between different genealogical platforms/programs/softwares. Last release is Gedcom 5.5 from 1996 and it is not going to be updated anymore.

It is only the events that is downloaded from a software and can be uploaded to another software. Textfiles stored outside if the software, like on your harddisk, will not be copied. Pictures will not be copied, only the link to where they are found. And different softwares uses different gedcom-tags, which could meen that some of the information you download from one software, isn't uploaded to the other software, because the two softwares aren't using the same gedcom-tags.

GEDCOM is not a good program to use as a backup of your genealogical information, you need a full, preferably offline, genealogical software to have a good backup, or you can do as I do, use your offline genealogical software as your primary one, and then use the online ones as secondary. The reason being that I can have backups of all the information from my offline software, while the online one the only possibility is to use gedcom, unless the online software has an offline part that can communicate with each other, like MyHeritage has.

To read more about gedcom: https://en.wikipedia.org/wiki/GEDCOM

Dear Mr. Pedersen,

You mentioned "need a full, preferably offline, genealogical software to have a good backup, or you can do as I do, use your offline genealogical software as your primary one, and then use the online ones as secondary", do you know of an offline software? That sounds like I can pass that down to my children and grandchildren. Thank you for submitting your advice.

At the bottom of the wiki-page about gedcom there are links to wikipages of several desktop (offline) softwares. Some are freeware, some are shareware and some you need to pay upfront, but I think you can test most of them before making a desition.

Of those mentioned there I would check out Brother's Keeper (which I use), Family Tree Maker, Legacy, The Master Genealogists (development discontinued as of 2015)

If you use Mac I would suggest Reunion, and if you use Linux you should go for Gramps.

Install testversions on your computer, add some 20-30 persons and check the program for how the reports look like and how they are to work in, and how the charts look like. Then chose one that you like and feel comfortable using. When you have chosen, you should stick to it, because usually the only way to emigrate your database to another software, is to use the outdated gedcom-format. So chose wisely.