I'd originally uploaded a font with the "free download" option. But now I would like to charge, how can I change this characteristic in my dafont account?
Please, I'd really appreciate the help!

Ale Bortoni, all of the fonts on Dafont are free to download. Dafont does not collect money oh behalf of any of the designers whose fonts are hosted here. Read below if you want to attach a licensing requirement, for commercial use.

Anyone who has uploaded a font at Dafont will have a link at the top of every Dafont Window named "My Account". Click that link, and on the page that shows your font(s), you'll see a link called "update" to the right of the name of the font. Click that link, change the information in the list box for "License", then click the "Submit" button at the bottom. You can also use the update link if you want to add some artwork, or add/ change the 'Note of the Author'.

If you want to make a change to the download file, (ie: add or update a read me document, change the font header to indicate that the terms of use have changed), you should upload a new version of the download .zip, with instructions to Dafont explaining the changes that you'd like to make.