I was a bed wetter until past my tenth birthday, although not every night and not always heavy, but would usually wake up as I started leaking. I wore training pants and plastic pants to bed from Sunday to Thursday nights as they were usually adequate enough to prevent my dribbling problems, but I wore a disposable diaper on Friday and Saturday nights as I would stay up late, be more tired, and therefore more prone to completely wetting the bed without waking up.
If my trainers got wet during the night, but my sheets were still okay, I'd simply just change myself. But my mother insisted on helping me put the real nappies on, as I never seemed to put them on properly. I outgrew the big baby diapers by age ten, and my wetting had virtually stopped as well, but I continued to wear the cloth training pants until I was 11 just in case.
So while it wasn't exactly getting "getting changed" as such, I have very clear memories of being helped into a disposable at age 10.
As for getting changed out of wet pants, I remember a few occasions.
Probably the most prolific one is around the age of 8, and wetting my pants at my aunts house while playing with my cousins outside. Mum called me over, and simply took my wet shorts off, leaving me in my wet underpants and sending me off to play again while she hung my shorts on the line to dry. Afterwards she took my undies off and put my now dry shorts back on me in the backyard. Nobody really batted an eyelid at it.
Another one was around the same age, 8/9, and being desperate to pee in the backseat of the car during a long drive. Dad wanted to wait until we got to the next town with a bathroom, but I couldn't hold on. I started to wet myself before he pulled over, and my sweatpants and briefs were quite wet by the time I'd jumped out and ran behind some bushes.
We were going to my grandmothers house for a few days, and the luggage was in the boot of the car. My mother had to dig a change of pants out, and she helped me to get changed in the backseat at the side of the busy road with the door open.
An earlier memory was me around 6/7, and actually waking up in my night nappy still dry, but wetting myself on the way to the toilet. Mum didn't panic, just made me stand still until I'd finished, then took my back to bed where she changed me into a fresh one.
I don't have any memories of being changed as a baby or toddler though.