pull down to refresh

This section of a post I published before the last UASF in 2017 may be helpful:
A UASF relies on the fact that it is not the miners but the economy of bitcoin users that set the rules of the bitcoin network by throwing their economic weight behind one rule set over others.
Once a UASF is enforced by a given full node, any blocks produced by miners that do not comply with the rules of the UASF will be rejected by that node. If enough economic nodes enforce the UASF, then miners will be strongly incentivized to comply with the rules so that they’ll be able to sell the bitcoin mined in their blocks (and avoid losing their block rewards in a reorg).
And this post is not specific to UASF but may help you build a better understanding of how consensus changes work in bitcoin: