Experience rate

No Experience points
ECL stands for effective character level, and is equal to the total amount of hit dice you have, plus any level adjustments you have. The entire group has the same ECL and levels all at once about every other session. Thus we do not use experience points. You cannot use experience points to fund items or spells.

Leveling in between sessions
When you level up, the DM will say so at the end of a session. You are then tasked with leveling up your character before the next session. Leveling up your character is not part of the session, the DM needs to be able to study character developments before the next game starts. If you enjoy theory-crafting with other players, some people like to stick around for that at the end of a session.

It is considered good practice to inform the group on the roll20 forum of important character improvements, such as cool new powers that you picked up.

Switching characters
A good DM should always be open to help a player who is no longer having fun with his character. In case of a character switch or character death, there will be no further penalties. Your new character will be at the same ECL as the party, even when taking over an NPC who would normally be much weaker or stronger.