In order to be able to posts pictures and have an avatar, you first need to become a full member because as of right now you are considered a new member. New members are restricted from starting new threads, posting pictures and links, having an avatar or changing one, sending private messages to other members. In order to become a full member, you will need to have 25 points, 15 posts and an account older than 24 hours. https://forums.thesims.com/en_US/discussion/978073/new-members-guide-welcome-to-the-forums
For any New members who want to get their post/point count up, the best thing that I would advise you to do is to find threads that may interest you and join in on them or go to the Off Topic section and join in on some of the word/story games over there. The posts made over in the forum section will go towards your post count whereas the posts made on your wall and the Activity Feed doesn't go towards the total post count. The only thing that you will get if you should make any post over on your wall or Activity Feed will be any Insightfuls, Likes or Awesomes as they will go towards your total points count. Hopefully creating your posts on other threads will also increase your points... https://forums.thesims.com/en_US/categories
And I would also suggest reading the thread about necroposting as well as there is a rule about it in the rules section. I would also suggest checking the title of thread as well as the location of the thread since we have older Sims games sharing this forum. An example would be if you're a TS4 player and have an issue with the game, please check to make sure that they thread that you have brought up isn't a TS2/TS3. I have provided links at the bottom of this post for "New Members" to be able to posts their issues in. https://forums.thesims.com/en_US/discussion/983366/lets-talk-about-necroposting-🧟
The EA team has moved The Sims 4 Help Center section to the Answers HQ Forums now. The Sims 4 Help Center section on this forum is now "Read Only". So you will need to click on this link if you have any issues that you want to report to EA and hopefully get the help that you need... https://answers.ea.com/t5/The-Sims-4/ct-p/the-sims-4-en
And for name changes, you can request them on @EA_Cade. @EA_Lanna will still be on the forums to help out when she can...