My dad downloaded it and he said it was a pain in the but to work and i never used the BBM till just a couple of weeks ago. Do I have to back up my BB before I downloaded it someone told me that I have to do that in order to keep my contacts.
One of the great features of BBM 5.0.0.xx is it backs up your contacts for you and stores it on the RIM server. I would also suggest signing up for the BlackBerry Beta Zone. You can then get the BBM 5.0.1.xx.
BBM 5.0 also improves several existing features. In other words, the older versions are fairly buggy with regards to file and picture transfers. Also, the Groups feature is very nice. Not trying to go off-topic but OP seems set on knocking something OP hasn't tried.
If I download Blackberry Messenger 5.0 and if I dont like it can I delete it and how to I get the original Blackberry Messenger.
To answer the question. I think I might load up a utility such as BBSAK and copy off the .cod and related files. Newer versions of BBSAK facilitate backing up installed apps and even creates a .jad file for easy reinstallation. This way you can retain your older version.