Batteries, exchanges

Hello guys, now I’m one of the lucky ones, with 2 batteries in the thick. The big power supply battery (AGM) is starting to “weaken” now, especially in winter with the heater. Is only a 3.2 V6, but with full equipment, so after almost 6 years it is allowed to give up slowly. Before the whole electronics starts spinning, I will switch. Does a train rip on the rep instructions from the manufacturer, because just attaching do not trust me? Over the batteri e is a fuse/relay box, which must also be released or at least that the battery goes in or out. Thank you FatOne