As Apple company makes pretty strict limitations on who can install iOS betas. So the only legal way for you to install iOS betas is to get your UDID (Unique Device Identifier) registered as an iOS developer. UDIDead tool  by StevetheRipper frees you from need to obtain the official iOS developer account (which costs $99/year) by simply creating the bundle of iOS beta, which could be uploaded to device using redsn0w.

There are two main procedure calls (arguments) within the UDIDead are:

- b 

to get the info about firmware build and

-f 

to get the info about firmware build Optional argument is:

-o 

to get the data about output directory

UDIDead Bundle Maker Download:

Official site Github clone

How to install custom Bundle to iDevice:

Step One: Get the latest version of redsn0w. Then run  redsn0w from command prompt or terminal using the -S argument (double check you're using capital S). Here is the expample for Mac OS and Windows users. Now click on Extras, then Select IPSW and find a path to the iOS firmware for your device. Step Two: Prepare your bundle using UDIDead. This should be an archive file. Then within redsn0w program click 'Jailbreak' and follow the guide for entering DFU mode.  Wait until you see a checkbox with custom bundle selection. Choose it, browse for your cooked bundle and click 'Next'. Step Three: After redsn0w finishes all the operations iDevice will reboot and activate through iTunes.