Upgrading a reward ticket

Hello
I have enough miles to book a return seat in Y to SFO later this year, but am hoping that by then I will have enough miles for PE.
Need to spend, spend, spend
Also there is no availabilty for PE at the moment.
If I book Y now will I be able to upgrade to PE if it becomes available nearer the time ? Will there be a charge for this ?
My dates are a bit flexible as I will be joining Mr L2H while he is there on business. Are there any days of the week that are good for reward availability in PE.
I would ring the flyclub helpline but not keen on being on hold forever [V]
Many thanks
L2H
I have enough miles to book a return seat in Y to SFO later this year, but am hoping that by then I will have enough miles for PE.
Need to spend, spend, spend

Also there is no availabilty for PE at the moment.
If I book Y now will I be able to upgrade to PE if it becomes available nearer the time ? Will there be a charge for this ?
My dates are a bit flexible as I will be joining Mr L2H while he is there on business. Are there any days of the week that are good for reward availability in PE.
I would ring the flyclub helpline but not keen on being on hold forever [V]
Many thanks
L2H