The default settings work for most people. There is a fundamental tradeoff between anonymity and performance. Tunnels longer than 3 hops (for example 2 hops + 0-2 hops, 3 hops + 0-1 hops, 3 hops + 0-2 hops), or a high quantity + backup quantity, may severely reduce performance or reliability. High CPU and/or high outbound bandwidth usage may result. Change these settings with care, and adjust them if you have problems.
Exploratory tunnel setting changes are stored in the router.config file. Client tunnel changes are temporary and are not saved. To make permanent client tunnel changes see the i2ptunnel page.