Update from one beta to another

First, you can do nothing until such time as the new Public Beta Programme is made available - unless you are a registered Developer.

For the iPadOS15 Beta programme, you will need to re-enrol when the Beta programme becomes available to you. After you have installed the new beta-profile, you should be able to install the new version.

The same requirement applies to Mac.

No, you do not need to delete all the data to update to the new beta.

No you should not need another computer or drive. Though you may want to keep the beta in a separate partition so you still have access to your non-Beta installation if issues do arise.

Also remember Betas are confidential, you cannot discuss them here at all. You are entirely on your own if you choose to install them.

Read here: https://beta.apple.com/sp/betaprogram/faq

Is the public beta software confidential?

Yes, the public beta software is Apple

confidential information. Don’t install the public beta software on any

systems you don’t directly control or that you share with others. Don’t

blog, post screen shots, tweet, or publicly post information about the

public beta software, and don’t discuss the public beta software with or

demonstrate it to others who are not in the Apple Beta Software

Program. If Apple has publicly disclosed technical information about the

public beta software, it is no longer considered confidential.

Read our Terms for full details

No Support and Maintenance; Future Products.  During

your participation in the Beta Program or in a particular seed, Apple

is not obligated to provide you with any maintenance, technical or other

support for the Pre-Release Software.  If,

at Apple’s option, such support is provided, it will be provided in

addition to your normal warranty coverage for your computer and/or

device.  You agree to abide by any support rules and policies that Apple provides to you in order to receive such support.  You

acknowledge that Apple has no express or implied obligation to announce

or make available a commercial version of the Pre-Release Software to

anyone in the future.  Should

a commercial version be made available, it may have features or

functionality that are different from those found in the Pre-Release

Software licensed hereunder.

Where did I mention that you have to delete anything? Your ability to update your iPad to a Beta version is controlled by the Beta Profile that is installed on your iPad when you enrol in a Beta test programme.

If the iPadOS15 Beta requires you to reset or first restore your iPad to a production version, the instructions that you receive when you sign-up will make clear any system requirements or prerequisites.

If you are already an established and bona-fide Beta tester, all this should already be known to you…