Is Uniswap immutable?

I've been hearing a lot about Uniswap recently, and it seems to be quite popular in the cryptocurrency space. But I'm still trying to wrap my head around some of its fundamental concepts. Could you clarify something for me? Is Uniswap immutable? I've read that it's a decentralized exchange, but I'm not sure how that translates into whether or not its code or functionalities can be altered. Would you mind explaining this to me? I'm really interested in understanding the nuances of this technology.