Not too often, I usually do it when I feel like my avatar/sig/title/collectibles are starting to feel a bit stale. Sometimes I might just do it if I'm bored though tbh
Like, rarely. I've kept my previous avatar and signature for a very long time, and I just recently changed it. I might try to spice things up a little bit and change it every now and then, though.
On average, I change my aesthetic about once a month. I actually had an N64/SM64 aesthetic for quite a while, but in the last few months I've changed it a couple times.
I'll probably have my current aesthetic for a while, though. I hear it makes people smile, and that makes me happy.
Avatar, twice a year at most
User title, I've only changed it twice
Signature, whenever I think of something interesting to put (so not to often)
Collectibles, usually seasonally
I almost never changed my aesthetic until recently, now im just saving bells so I can upload a gif and be done with this (Then I can start collecting mittens again)