How would I update iOS 7 betas once new ones are released?

I don't have a developers account however I registered my UDID but I want to know if I
can update my iPhone the regular way (I.e settings in iPhone/iTunes on the computer) or will I have to go back and download the IPSW file again. But I'm afraid I will lose my data and stuff if I do it that way again. Will I?

Easy, just go to apples website when the beta comes out and you should be able to find it pretty easy knowing how apple is, most likely it will be plastered all over their main website.

As long as your UDID is regisered, you shouldn't have a problem. I registered mine at http://www.instantudid.com/ for $5, to get iOS 7 working on my 4S.