Help required for finding out upgrade options

I'm looking for some advice and being pointed in the right direction to find out my options.
I've checked rewardseats.com and found that I can fly from London to either SFO or LAX in upper class using 100,000 miles I've collected.Final destination is Las Vegas which has no reward seats on my dates.
I've read a few posts (but cant find them again in the search) where people discussed the option of buying a premium economy seat and then upgrading to UC using miles, so you can still earn miles for the flight.
My query is what are the bucket codes I require to upgrade from PE to UC and where can I check availability?
The fact that I can get a return reward flight for 100k miles does that mean I would be able to book an upgradable PE and use miles to upgrade to UC if there was an upgradable PE seat?
Do I need to use expert flyer? my free trial ran out, so is there another website where I could check bucket code availability for specific flights?
And can you go from an upgradable economy ticket, and upgrade to PE and then UC?
Any help is greatly appreciated.
I've checked rewardseats.com and found that I can fly from London to either SFO or LAX in upper class using 100,000 miles I've collected.Final destination is Las Vegas which has no reward seats on my dates.
I've read a few posts (but cant find them again in the search) where people discussed the option of buying a premium economy seat and then upgrading to UC using miles, so you can still earn miles for the flight.
My query is what are the bucket codes I require to upgrade from PE to UC and where can I check availability?
The fact that I can get a return reward flight for 100k miles does that mean I would be able to book an upgradable PE and use miles to upgrade to UC if there was an upgradable PE seat?
Do I need to use expert flyer? my free trial ran out, so is there another website where I could check bucket code availability for specific flights?
And can you go from an upgradable economy ticket, and upgrade to PE and then UC?
Any help is greatly appreciated.