Step by step:
1. If MAT is open, close it. Changing the password can be done from an already open MAT, but my instructions are easier starting from the top!
2. Start MAT !!
3. Click the + to the left of your Site Name
4. Right click the System Name and left click {Properties}
5. Click the <Customer> tab at the top right
6. Click the [Properties] button.
7.In "Scheduler System ID", you will find User ID and Password.
Hope this helps.
(MAT and OTM are NOT evil creations of satan! I use every tool available - CLI, MAT, OTM, ProComm, HyperTerminal - whatever makes the task at hand easiest. You just need to keep in mind how they all play together)