new 2.6 version Login issues

I believe I have no choice but to use the latest version of WordPress if I setup on cpanel as it pretty much does the job on its own.

I have been using 2.5 or 2.51 not sure which, but I have had no problems at all with this older version.

Question is – can I ‘down grade’ from version 2.6 to the version I have been using without problems ?