I think, bettery change karna itna b mushkil kaám nai hai, jitna bnaa dia gya hai.
Following is a very simple guide to properly replace car battery:
Just follow it, and you are good to go. If tracker is not installed, then it becomes even more easy.
Max. which can happen during this time is; some readings gone (like Trip A, B, Fuel efficiency, etc.) and idle relearn may be reqd, which are again; not a big issue.