However, I realised I misread what this person was asking. In essence, he was asking about how to connect the strumming pattern between chords so that it sounds smooth when changing from one chord to another.
To answer this, we will have to take a look at the strumming patterns that I have previously posted in my post regarding strumming patterns. They are:
1 2 3 4 Pattern 1 : D,D,D,D,DU 1 2 3 4 Pattern 2 : D,D,DU D,D,DU 1 2 3 4 Pattern 3 : D,D,UDU,DD,DU 1 2 3 4 Pattern 4 : D,UDUD,UDUD,DU 1 2 3 4 Pattern 5 : D,DU,UDU3/4 Songs
1 2 3 Pattern 1: D,D,D,DU6 /8 Songs
12 3 45 6 Pattern 1: D,UDUD,UDU
What I failed to explain is that you should take note of how each strumming pattern ends with a "DU". This is in fact the connecting strum to the next chord. So, what I usually tell people is that at the last "DU" that you see, you can start changing to the next chord. Your right hand will just be strumming the DU while your left hand is changing to the next chord. So, you would have changed to the next chord by the time you start your strumming pattern again. This is how you achieve the smooth and connected sound when changing between chords.
So, don't wait till you finish the whole strumming pattern, then change to the next chord. Instead, begin to change at the DU. Also, you do not have to upstroke all 6 strings. In general, all the upstrokes should only hit the first few strings eg. 1st and 2nd string.
Hope this has answered your question.