Originally Posted by freakinvibe
On BES there are SP (Service Packs) and MR (Maintenance Releases). The SP are the "big" upgrades and the MR are the "small" upgrades within an SP.
If you are on 5.0.1, you are on SP 1. If you need to upgrade to SP 3 ( ==> 5.0.3), just download the SP 3 Upgrader and install it. After that, upgrade to the current MR level (which is MR 4 at the moment for full BES and MR1 for Express).
Just make sure you get the proper SP or MR for you version of BES. Full BES and BES Express are similar but different.