The message-centre is located in your profile. This is by default by the software that I use.
You van alternatively open a new window by clicking on “private message” while you hold down the ctrl-key (cmd on mac). Then you get a new window or tab where you can write your message which you can close again afterwards.
Your profile you can change here: https://www.aspie-singles.com/members/sarahgrace/profile/edit/group/1/
Your profile photo here: https://www.aspie-singles.com/members/sarahgrace/media/7/edit/#media
I have changed your profile pic for you by the way. I saw you had uploaded it to your album.
You can change all these details on your profile. Just scroll down in your profile. There you see the first tab which is called “activity” and the next one is “Profile”. It is there where you need to be.