(Dorico newbie here…sorry for the elementary questions but I have done my searches and don’t easily find answers)
In this 4/4 measure below, I’d like to change the last note from a quarter note to a half note. But if I double-click on the quarter note, both the quarter and its preceding 8th highlight, and I can’t find any simple/easy way to do this like I used to do in S*******. 
I welcome shortcuts, as I’d like to get up and moving faster with Dorico.
With the tie chain selected, press Alt-Shift-right arrow to extend the duration.
Ah. I see why you are Grand Senior. Thanks!
The reason both notes are highlighted is that in Dorico, tied notes are really just one note that’s notated as a tie depending on its duration, position in the bar (Dorico automatically splits notes into ties across the half-bar, for example) and position relative to barlines (similarly Dorico splits notes into ties when they extend across bars). So instead of thinking of “changing the quarter note to a half note”, in Dorico you can instead think “I want to lengthen that note by a quarter note”, and the key command Dan described does just that. If necessary, Dorico will renotate the note as appropriate for its new duration.
You can control how notes and ties are split on the Note Grouping and Beam Grouping pages in Notation Options (press Ctrl/Cmd-Shift-N), which sets your defaults on a per-flow basis. You can also use Force Duration locally to specify exactly what note durations you want displayed if necessary.
(If you ever want to put something in the middle of a tie chain, like a dynamic, show the note input caret by pressing Shift-N and press Space/the arrow keys advance the caret to where you want the e.g. dynamic to go, then input it with the caret still showing.)
Thanks Lillie.
I understand…and then I don’t. I continue to work forward in my project and I have this measure (again, in 4/4):
This time, the durations are correct. I don’t need to make anything longer. I just need to tie together the last two notes (sixteenth to the dotted half).
When I select the last sixteenth note and hit T, it re-writes the passage to sixteenth tied to quarter tied to half.
If the answer is in Notation Options, I’ll need help figuring out exactly which setting is overriding what I want here, because I don’t see it (and it’s particular to the notes being tied, since, as you can see in my first screenshot, it’s drawing it correctly if not tied).
There are separate notation options for notes starting on a beat and spanning multiple beats versus those that start off the beat and then span the half-bar. If you don’t want Dorico to show the half-bar there and you can’t find a combination in Notation Options that produces exactly the result you want in all circumstances, you can then use Force Duration, which tells Dorico that it must notate the note (or rest) exactly as you specify, rather than allowing it to be subject to Notation Options. You might be tempted, as somebody coming from Sibelius, to just switch Force Duration on and leave it on, but I really strongly advise against it. When you force the duration of every note, you tie Dorico’s hands so that it can provide less assistance to you when you subsequently shift your music rhythmically, or insert additional notes, or re-bar in a new meter. So you should use Force Duration only when you really need to. You can read about Force Duration here.
While he is extremely knowledgeable and erudite, that has nothing to do with his being a grand senior member. That disctinction has to do solely with how many times he has posted. When you have posted several thousand times you will ALSO be a grand senior member, whether you are knowledgable and erudite or not!!! 
I am eagerly waiting to see whether, when Leo reaches 10,000 posts, he will turn into Daniel at Steinberg. 
(Probably not: there can only be one of those.)
There’s a title called “Forum Elder,” held by a Cubase guy with something like 15,000 posts. Oy.
I’d ask him if he has a life outside of Cubase. 
Hmm. Martin (the forum elder) has his website listed as www.cubase-training.com, and has been kicking around here since 2011. Unless I stop playing the piano and entirely rebrand as a Dorico trainer I can’t see my post count rising anywhere near his level.
And no, there can only ever be one Daniel at Steinberg (though I’m sure that in the real world there are many Daniels at Steinberg).
Well, I suppose Forum Elder is better than Grand Senile Master, which someone joked about (was it Leo?) when Leo first reached that level.