Hi there,

You can change the slider text color via Appearance -> Customize -> Theme Options -> Slider -> Content Color

The size of the slider text can be changed inside the textarea where you add the slider texts by wrapping your texts inside the following code:

<span style="font-size:16px;">Your slider texts here</span>

You can change the 16px font size to your own needs.

Hi there,

The slider image size (which depends the height of the slider) is defined inside the functions.php file. You can change this size on 3 ways:

1. By installing the child theme (located inside the full download package on ThemeForest) and overwrite the slider image size in the child theme functions.php file

// Jumbotron Slider Sizes
add_image_size( 'physio-qt-slider-l', 1920, 715, true );
add_image_size( 'physio-qt-slider-m', 960, 358, true );
add_image_size( 'physio-qt-slider-s', 480, 179, true );

2. By installing the Simple Image Sizes plugin.
After activating navigate to Settings -> Media and change the sizes of the following fields:

physio-qt-slider-l
physio-qt-slider-m
physio-qt-slider-s

Please keep in mind that the L size is used for dekstop, the M size is used for tablets and the S size for mobile screens.

3. Manually scale the image with a image editor program/software. Please make sure the image is 1920 px in width and you can set a custom height to it. 

After the sizes has been changes you need to install the Regenerate Thumbnails plugin.  Via Tools -> Regen. Thumbnails you can apply the new image size to the images by pressing the button on that page. After the plugin is finished regenerating you can delete the plugin.

Unfortunately this is cumbersome because this is how the WordPress core handle image sizes.

If you're looking for more slider options or more advanced options I recommend to take a look at the (free) Crelly Slider plugin, which is compatible with the theme.

Let me know if you have any questions.