How to deal with early c4-c5/c5-c4?

The drawback of such moves is releasing the pawn tension. In these examples, pushing the pawn has removed the possibility of exchanging pawns on d4 or d5. You play the closed position as with any closed position, or you attack the base of the pawn chain where weak. For example, in the 2nd diagram, you may consider long-term ideas like Nbd2 and then e4 with your pawn to fight for the center and now the c4 square and e4 square are being contested.

Also, a standard plan in such a position where black's pawn is on c4 is, unless you have a 'hole' on b5 (example, if black's a7 pawn is on a5, then you can play a2-a4, and Nb1-c3-b5), is to play c2-c3, which stops black's c-pawn from advancing further and which overprotects your d4 pawn, then "undermine" the head of the pawn chain with b2-b3. This undermining prevents Black from attacking your c3 pawn with the move b7-b5-b4, and can lead to the changing of the pawn structure (e.g. c4xb3 a2xb3 leads to the opening of the a-file, and may lead to a favorable c3-c4 or even the pawns remaining stationary while you attack the kingside).

For white playing c4-c5, it's the same thing in reverse. Black often counters with ...c6 then ...b6. Sometimes ...c6 can be omitted, but there may be problems with the c6 square (tactics involving checks and the Ne5 move), so it's quite often a good idea to play ...c6 then ...b6 if the position permits.

Putting knights in front of the advanced c-pawn to "blockade" it can only work in certain situations, as otherwise they get exposed to further pawn pushes of the b-pawn and a-pawn storm.