if I understand well what knightdk said, blockchain can not grow more than 144 Mb a day as 144 blocks of 1 MB are generated per day as a maximum. is that right?
Using the current protocol rules, yes.
Howerver, if block size increases (as a decision of the miners)
No.
Block size can't increase as a decision of the
miners. It requires a consensus of the
users. Everyone running a full node must agree.
or if number of blocks generated per day increases (don't know if this is possible),
It is possible if a significant amount of hash power is added to the network shortly after a difficulty adjustment. However, it will adjust automatically back to 144 blocks per day again one 2016 blocks have been completed since the previous adjustment.
Creating a permanent change in the average number of blocks per day would require a change to the consensus rules (which would require the consensus of the users).