Ok. I ride a 52x19 which is 73.2 gear inches it's always been pretty good until I moved to Glasgow, Scotland a year ago and I find myself struggling on some hill climbs. Now I'm thinking of switching out my chainring to a 48-50t but I'm not sure how much of a difference it will make. Would a 48t (67.6g.i.) make it feel like I'm pedaling in the air ? or a 50t which is 70.4 g.i. be better ?....pretty much I'd like something that's a bit easier than what I have now and can't decide..how much is too little or etc...
I hope some of you have experience in this because my knees are aching !

Well, you could take my experiences with a grain of salt, but perhaps they will provide some insight that may be of help to you.

I'm in a relatively hilly area so I started running a 45x16 (73.9 gear inches) that really wasn't agreeing with me. After acquiring another bike that got all the doner parts from my 45x16 setup, I decided to set up my original bike with a 42x18 (61.3 gear inches) setup. Pedaling up the hills with 61 gear inches feels MUCH easier in comparison to 74. On the flats, it's quite obvious that I can't reach speeds similar to my old 45x16 setup.

In retrospect, had I only been able to make minor drivetrain adjustments for easier climbing, I would have chosen a combination of gears to only drop 3-5 gear inches. If you don't want to sacrifice speed on the flats in place of easier climbing, I'd suggest you do this.

I'm new to FG bikes having ridden it for only 5 months, but I'll share my experience anyway. I started out with 42x15 (76 GI) but found out after a 60 km ride on rolling hills that I might be better of with a lower ratio. Have been running 66.7 GI (42x17) and I find it is much easier to do longer rides with hills.

The only downside is that I spin out on downhills at ~42-44kmph.

Here is a typical elevation profile.

Just curious why you want to switch your chainring instead of cog? Going to a 20t would give you ~70 & 21t ~66.

Well the chainring could use the replacing..and the cog is new. I've decided I'll be going with the 48x19 and it seems that's what most ride here anyways. Thanks for the help.