Switching to a new Core?

[Atlamillia]

I'm currently using a 3.3.5a Arcemu repack for my server and i've been looking into switching to something more stable, and easier to use.

My problems with this are:

A) How do I go about switching?
B) Will this affect my database spawns and such? (I use HeidiSQL)
C) Which repack should I switch to and where would I find it?

[Appled]

I'm assuming you want to switch to TrinityCore.

Switching a core to another usually forces you to create fully a new database. In other words, you would lose everything you have created by yourself. There may be some programs which are created just for this case but I do not know of their existence. Also, if you have some knowledge of SQL, you are able to dump the data from arcemu database, change the code structure with notepad++ for example, and then execute the data in TrinityCore database.
I don't know what repacks there are but you should study how to compile the source code by yourself. Why? You can easily get the latest updates from TrinityCore and also you are able to edit the source code as well. For reference, I present you TrinityCore's wiki page: TrinityCore Home - TrinityCore - KPsN Collaboration Platform

In addition, HeidiSQL is not a database. It is a software which makes database browsing simplier. Other softwares are Navicat and SQLyog.