I really want to upload my own photo onto my profile but I don't know how could anyone help me?

Click user profile on top right of screen, click edit profile then click avatar in the left panel.

HI.
Click on the User Control panel link at the top of the screen. Then select the Profile tab. From here choose Edit Avatar and add your picture. Don't forget to save(submit) before you exit. And there you have it.

I think I recognise this. I also am a bit confused; how do you change it on text adventures.co.uk? Sure, I can change it here, but I see that some people on text adventures have pictures. How do I change mine?

People with pictures have signed in using a facebook account.

You can also set your profile picture using Gravatar: https://en.gravatar.com/ - if you use the same email address of course.

At some point soon I'll add a way to upload a picture manually.

I made an account there, but I'm not seeing an option on this site to sign in with it?

Wait never mind it is working, I'm dumb.

I'd worry about what other places the avatar would appear on lol.