You cannot change it. Strings with the user name in the URL were used in the "old times", but the system was changed to the cryptic IDs later. Besides others also because of privacy reasons (many users putting their true names, emails or other sensitive data as their login names), and because of securty reasons.
Another important reason is that there are millions of users, and therefore also countless people sharing the same user name, hence the unique ID is a necessity altready for that reason alone.
And yet another reason is, that the user has the possibility to change his/her user name anytime. If it directly impacted also the login URL, it would have serious consequences, and would render existing links dysfunctional. If only the original login name was used in the URL, it would be even more confusing, and potentionally revealing information (i.e. true name) that the user decided to hide.
but it's not possible.
Yes, it is possible. Go to your profile, click Edit Profile, and change the name and/or upload a photo: