I recently purchased a brand new polo r line, I'm wanting to change the original 16inch to 17inches, my question is would their be any mechanical adjustments needed or any onboard computer settings need to be changed. secondly what are the effects on the car i understand it changes gear ratios and speedometer accuracy? thank you.

Depends on what tyres are on it currently and what tyres are being fitted to the 17s

First welcome to the forum.

As stated above, it all depends on what profile the new tyres will be, if you retain the same profile as the 16" then you should recode the ABS controller due to the greater rolling circumferance

Are the alloys you have on the car currently 215/45/16?

Id suggest looking into a 215/40/17 tyres for the new alloys. There is only a 4mm difference in diameter which is less that 1%, so shouldn't effect anything.