A moderator declined two of my flagged comments and I disagree with this. How should I proceed in getting this reversed?
You post here (on meta) explaining what you flagged and what the response was, and ask why the decision was made that way and whether it was the right decision.
Of course there is no guarantee the decision will be reversed, but if not, you'll get an explanation on why it was the right decision in the first place.
You shouldn't set too much store by declined flags. If you look on MSO, it happens relatively often that flags are declined and yet the action gets taken. There's two outcomes that can come out of this sort of thing.
First of all, did the action get taken? If it did, then no worries. If it didn't, what was it? If you were asking for removal of comments, then don't worry too much about it - comments are temporary anyway. If you don't like a comment but it's not offensive or anything, well, shucks.
The only thing a declined flag really does is it slightly affects your flag weight - that is, your total helpful vs. declined flags. This is not something to worry about unless a really large percentage of your flags get declined. This is used by mods as a very rough measure to help gauge the importance of flags.
All in all, there's not all that much to decry about a declined flag.