Thanks. I have the costing clarified now.
Some constructive feedback - I have been a very happy customer for many years, but this to me doesn’t feel right. I am disappointed.
At the moment you are participating in the Winterfest festival with a 25% discount. Does this apply to an upgrade from Standard to Pro ?
Yes, of course, the WinterFest discount also applies to upgrades.
How can I do that?
Well … visit our homepage. Check out the WinterFest link. It should be obvious 
Although, if like me you thought the cleverest way to figure it out was to visit the official WinterFest homepage, and didn’t even think to look at the blog on the DT page, you might now feel a little silly (especially if you pride yourself in your ability to search the web) 
Anyway, seeing as I’m slightly embarrassed, here is a direct link to the blog entry for anybody else who’s brain works the same way as mine.
It isn’t obvious. It is non obvious and unclear. 
The winterfest page takes you to the full price with 25% discount ($149) not the upgrade version.
It would be great if you could kindly tell me a link, or a process to facilitate applying the Winterfest discount on the upgrade from Standard to Pro.
only you can try as you are the buyer but does not the discount code kick in for checkout of that upgrade you are purchasing?
Check my link above; there is a discount code in the blog post; you can log into your account, select the upgrade, apply the discount code to the cart 
The link you are referring to is the one I was using. It takes you to the Pro version with 25% off. ($149). I am logged into my DEVONthink account.
I can upgrade for $99 without using the Winterfest discount.
The Winterfest link takes me to a purchase for $149.
What I am asking is for a process to apply this 25% discount to the upgrade price.
Empty your cart. Select your current DT license in your account. Select to upgrade that license for $99. Apply the discount code from the blog post by entering that code where the cart offers you the option to enter a coupon code. I’ve actually tested that for you in my account and it works. Don’t follow the links in the blog post or from the WinterFestival site.
What is obvious to one is often not obvious to the other. I’m glad it’s worked for you now 
Can I use the Black Friday discount to upgrade from the standard version to the server version?
Because bundlehunt is selling DevonThink Standard, I would like to purchase the Standard version first and then upgrade to the Server version during the Black Friday discount. Can I apply the Black Friday discount to this upgrade process?
Yes, licenses purchased from BundleHund are regular licenses that can be upgraded for a reduced price in any promotions that apply also to upgrade (not e.g. the students & educators discount).