Looks like you may have committed all the cardinal sins in a single slam dunk.
Creating and compressing and then scaling bitmap images which include rendered text is asking for trouble as it will always look “blurry”.
I would recommend removing your text and uploading just the blue background as your slider image — and then adding your text in the slider options.
But if you want to include text in an image, you could minimise the “blurriness” by:
a) using an image editor such as Photoshop which allows you to choose from various anti-aliasing options when rendering type onto a halftone image: “crisp” on “none” would be the best type anti-aliasing for small images – but anti-aliasing is really nothing more than organised “blurring” to remove the jagged edges of the curved parts of your text…so it’s not a perfect start;
b) your image is a JPEG and that’s a disaster compression algorithm for rendered text as it further softens edges and adds noise to help it disguise the fact that it is throwing away a lot of your image data; try PNG instead – or best-for-text GIF if your background image survives intact;
c) allowing your rendered text to be scaled up in size by the Customizr full-width slider is asking for more trouble as the artefacts/”blurriness” which is less visible at 1170px wide becomes unmissable at larger sizes; so either don’t use text in your image at all — or don’t use a full-width slider as your text will look fine in an 1170 x 500 framed slider.
Incidentally, the recommended size for a full-width slider image is 1200 x 500. Changing your image to this size would help a little but won’t solve the problem.
You might want to experiment with an extreme width image, eg 2000 x 500 which would help your text to display better but might introduce unwanted white space around the slider in smaller viewports as the image is scaled to fit.
