1st i will show you how to make your avatar a circle avatar in memberlist.
Go to the memberlist_user_avatar template and replace all the content with this :-
if you want to make your avatar size bigger than just customize the hight and wdith in the style...
as default i have height:30px and width:30px
you can increase it.
2nd. If you want to make your avatar, round avatar in postbit then prefer this guideline.
Go to the memberlist_user_avatar template and replace all the content with this :-
<img src="{$useravatar['image']}" style="margin-top: -20px;width: 30px; height: 30px; border-radius: 400px; transition: all 1s;text-align: center;" title="{$mybb->user['username']}" onError="this.src='{$mybb->settings['bburl']}/images/default_avatar.png';">if you want to make your avatar size bigger than just customize the hight and wdith in the style...
as default i have height:30px and width:30px
you can increase it.
2nd. If you want to make your avatar, round avatar in postbit then prefer this guideline.