2006 gpx250f19

Hi all I'm new to motorbikes n this site iv just bought a gpx with only 300 km on the clock and 100 are mine was just woundering if it is normal for the bike Jo jump forward a bit whin it's cold and put into 1st ? Also I. Read things about jetting kitS also exhausts are these mods worth the$ or would I be wasting my money? Thanks any other tips or advice would be good as I said new to it all