<p>default is 49</p>

<p>how to edit to higher?</p>

You will need to issue the following command (connected as a user that has alter system privileges, sys will do it)
alter system set sessions=
numberofsessions
scope=spfile;
Have you been getting an ORA-12516 or ORA-12520 error?
If so it's probably a good idea to increase the number of processes too
alter system set processes=
numberofprocesses
scope=spfile;
IIRC you'll need to bounce the database after issuing these commands.
This link
http://www.oracle.com/technology/tech/php/pdf/underground-php-oracle-manual.pdf
has some good information about configuring XE.
I consulted it when I ran into similar issues using XE.