Hi everyone, i have seen this questions asked many times and even by myself and there is no clear answer out there (or none that i could find on google) Firstly there is no convert lead form in the community edition (version 6 anyway) To convert custom fields in the lead section to the contact/account sections all you have to do is this.

1 Studio > Leads > Fields - Create your custom field
2 Studio > Leads > Layouts > EditView - Add your custom field
3 Studio > Leads > Layouts > DetailView - Add your custom field

so thats your lead form done, now move onto the contact

4 Studio > Contacts> Fields - Create exactly the same field type and field name you did in step 1
5 Studio > Contacts> Layouts > EditView - Add your custom field
6 Studio > Contacts> Layouts > DetailView - Add your custom field

so thats your contact form done, now move onto the accounts repeat steps 4 to 6 in the account section in studio. It is that simple, no coding or anything. The documentation out there is very confusing cause it points to the "convert lead form" in studio which does not exist in the community edition.

This might work for opportunities as well but i have not tested it.