How To Reset My System Without Delete Files?

[wen9x88]

How To Reset My System Without Delete Files?
last week i changed a lot setting and make my internet faster.
but it not stable,and i want to changed it back.
but i cannot remember all the setting.
i changed something in regedit,firefox "aboutconfig" and many many to make my internet and system run faster.
anyone how to reset it ??
thank you so much and sorry because my english suck~~~

 

[Tedster]

use system restore. Or use norton "GOBACK" which is far better.
or backup frequently to a second HD and restore from those files.

 

[wen9x88]

i think it too late to backup or restore system,because never install the norton" GOBACK" and create a restore point.