If you have already linked your Guild Wars 1 and Guild Wars 2 accounts, them when you log into your GW2 character, you should have an item called the Hall of Monuments Portal Stone, which looks like this:
Follow these steps as outlined in the Hall of Monuments Support article:
How do I get my Hall of Monuments rewards?
First, you need to link your Guild Wars and Guild Wars 2 accounts. Once you have done that, and providing that you have established a Hall of Monuments in Guild Wars: Eye of the North, then each character on your account will possess a Hall of Monuments Portal Stone in their starting inventory. Take the following steps to claim your rewards:
Use the Hall of Monuments Portal Stone to be transported to the ruins of the Hall of Monuments.
Speak with the NPC named Kimmes the Historian.
Review a list of items for which you have qualified.
Select any you wish to use on this character.
Return to your place of origin by using the Hall of Monuments Portal Stone.
If you do not see the HoM Portal Stone in your inventory, you can follow these instructions:
I do not see a Hall of Monuments Portal Stone in my inventory.
If you have linked your accounts and wish to access the Hall of Monuments, you can use the Portal Stone in your inventory to do so or you can obtain a Portal Stone by following these directions:
In Lion's Arch, head northwest into Hooligan’s Route.
At the Undermarket Point of Interest, find the charr karma merchant named Scornheart.
View Scornheart’s offerings and, on the second panel, select the Hall of Monuments Portal Stone. The stone is available at no cost.
Use the Portal Stone to access the ruins of the Hall of Monuments.
The stone is account bound, not character bound, so you can put it in your bank and use it on other characters.
As of the headstart, there are currently known issues with the HoM Portal Stone not showing up for many people and also with people having trouble receiving items from Kimmes the Historian. Reportedly, some people have fixed this by logging into their Guild Wars 1 account and then logging back into Guild Wars 2.