Is it possible to do it without buying root explorer? If so how?
Yes.
It's how I did it.
I think this is the steps I did (this is something I only do about twice a year, so I have to figure out each time)
1. open ES File Explorer, go into menu>settings. Change home directory to / and check Root Explorer AND mount file system under root settings
2. back all the way out of the app, and load it again from the applications folder.
3. scroll down to the build.prop file, long press and select properties. Hit the change button and make sure everything in the "write" column is selected. hit ok.
4. tap on build.prop and open it in ES Note Editor, scroll down till you find the "ro.builb.fingerprint" line and edit it to match
ro.build.fingerprint=verizon_wwe/inc/inc/inc:2.3.4/GRJ22/222219:user/release-keys
(i just had change the numbers right before the :user/release-keys to 222219, but you're rom may be different).
5. when that's done, hit menu>save. Then exit. Restart the phone.
6. post on here about how it didn't work, and I'll try and work it through with you.
There you go.
Add step 0. Download ES File Explorer from market

worked perfectly!