Your pension payment increases annually in April.
There's a system called the 'triple lock' in place, which means every April the state pension amount increases by the highest of the previous September's inflation rate (based on the Consumer Prices Index), the increase in average earnings, or 2.5%.
The triple lock only applies to your basic state pension entitlement. If you get an additional 'protected payment' on top, this will increase each year in line with inflation.
It's also worth noting that your pension may not increase every year if you retire to certain countries outside the UK.