Last night while playing the game, when we draw a Westeros card which says '' Supply '', we tried to make some of it. Ok, we moved our barrels according to the barrels we have on the board but the question is, while increasing the size of the armies - I mean that we are going to add more soldiers to the board - according to what we should arrange the new armies? 

For instance, while increasing the armies, I chose just knights and apart from that, my footmen were still out of war, so in this case I or anybody can choose the best option on the battlefield ( they may just choose knights firstly ).

Is there any rule to arrange this thing? Or was I playing correct ? 

Thanks so much.

You neve ADD units to the board during Supply.  Units are only added when Mustering.

"Reconcile Armies" means you REMOVE Units from Armies that are too big if your Supply went down.

Rules, Page 8

After a player adjusts supply, he must ensure the actual number
(and size) of his armies on the game board do not exceed his
supply limits. If his armies do exceed new supply limits, he must
immediately remove units from the game board until his army
number (and size) conforms to that allowed by his position on the
Supply track.

alright, now it is clear. thank you so much ;)