How do I change the default text in dropzone.js?

Add an element within your dropzone form as follows:

<div class="dz-message" data-dz-message><span>Your Custom Message</span></div>

You can change all default messages with this:

Dropzone.prototype.defaultOptions.dictDefaultMessage = "Drop files here to upload";
Dropzone.prototype.defaultOptions.dictFallbackMessage = "Your browser does not support drag'n'drop file uploads.";
Dropzone.prototype.defaultOptions.dictFallbackText = "Please use the fallback form below to upload your files like in the olden days.";
Dropzone.prototype.defaultOptions.dictFileTooBig = "File is too big ({{filesize}}MiB). Max filesize: {{maxFilesize}}MiB.";
Dropzone.prototype.defaultOptions.dictInvalidFileType = "You can't upload files of this type.";
Dropzone.prototype.defaultOptions.dictResponseError = "Server responded with {{statusCode}} code.";
Dropzone.prototype.defaultOptions.dictCancelUpload = "Cancel upload";
Dropzone.prototype.defaultOptions.dictCancelUploadConfirmation = "Are you sure you want to cancel this upload?";
Dropzone.prototype.defaultOptions.dictRemoveFile = "Remove file";
Dropzone.prototype.defaultOptions.dictMaxFilesExceeded = "You can not upload any more files.";

When creating the dropzone you can set the default message like this.

var dropzone = new Dropzone("form.dropzone", {
   dictDefaultMessage: "Put your custom message here"
});

Then

$('div.dz-default.dz-message > span').show(); // Show message span
$('div.dz-default.dz-message').css({'opacity':1, 'background-image': 'none'});