'02 TDI battery trouble

2002 TDI beetle - automatic - 64k miles. Starter cranks really weak and won't start. Tried jumper cables - still didn't start - I assume bad battery.
question -
I've heard if i replace (disconnect) the battery the computer won't function properly and will need to be reset. Is this true and can I do it?
Also, how difficult is replacing the battery and any tips? I've changed many battery's but this one looks like a beast!

any help is appreciated

That's a bit early for the battery to die, I'd get it tested first. There should be no problems with disconnecting it, your clock & tripmeter will probably reset.