The question is asking you to select the priority of "Acceptance(受け uke )" and "Change(変化 henka)".
Red5 is completely detached tile(浮き牌 ukihai). As you know if you want to reduce shanten number to close tenpai, Red 5p is the candidate.
But at this stage(early stage), I would select "Change" due to red 5p is very strong detached tile for "Change".
Once I select "Change", It should think maximum return. In this hand, tan/pin/sanshoku/ipe/dora2 is haneman without riichi.
I would aim folllowing 1 shanten. It is also maximize Acceptance of sanshoku(345 or 456)
Depends on the tsumo of sozu and pinzu, I would discard 3m or 6m.
4p is sitll ok with 3p or 5p or 6p.
So that this point of view,
is best for me to discard. because it is not related sanshoku and it has been followed by up 5b already for mentsu. it means discarding from
If I give up red 5p, the max value is tan/pin/ipe without riichi, 3,900. it is big gap of haneman prospect. it is worth to "Change"
If red 5p is just normal 5p, still I would keep 5p. If not dora and not red5, I would discard 5p.