If i remember correctly then it was the intend of satoshi to increase block size when bitcoin becomes more popular. Since he had to disappear before bitcoin became popular enough for problematic high fees there was never an adjustment. Now we are stuck with a lobby of miners that always say that everything is still "so cheap compared to a visa card" that we will probabyl have to live with those fees forever.

It can be phased in, like:

if (blocknumber > 115000)
    maxblocksize = largerlimit

It can start being in versions way ahead, so by the time it reaches that block number and goes into effect, the older versions that don't have it are already obsolete.

When we're near the cutoff block number, I can put an alert to old versions to make sure they know they have to upgrade.