syncing a current i phone with a new laptop with fresh i tunes install

New laptop, new i tunes install.Want to add/replace/sync songs to current i phone. The iphone goes through the motions of syncing but doesn't update music at all. Manual management tells me it will erase all the contents of my phone if i proceed Not too bothered about music only as Itunes has my new up to date music library but i only want to add/replace music.Will i lose anything else in the sync?

I would like to pair my phobne with the new laptop without losing any apps/contacts etc? Get nervous when the 'erase' warnings come up

HELP