The comments are controlled by the comment_form.tpl template
/modules/jrComments/templates/comment_form.tpl
They are set by default to show 500.
You can change that in the templates by going to
ACP -> USERS -> USER COMMENTS -> TEMPLATES -> comment_form.tpl
Then MODIFY and search for this line:
{jrCore_list module="jrComment" search1="comment_module = `$jrComment.module`" search2="comment_item_id = `$jrComment.item_id`" order_by="_created `$_conf.jrComment_direction`" limit="500" profile_owner_id=$profile_owner_id}
The
limit="500" is what your after. Change that to whatever you want.
eg: changing it to this:
{jrCore_list module="jrComment" search1="comment_module = `$jrComment.module`" search2="comment_item_id = `$jrComment.item_id`" order_by="_created `$_conf.jrComment_direction`" page=$_post.p pagebreak="2" pager="true" profile_owner_id=$profile_owner_id}
would give you 2 comments per page and a pager visible to move to the next page.
The full details for jrCore_list can be found here:
"{jrCore_list}"
http://www.jamroom.net/the-jamroom-network/documentation/development/89/jrcore-list