if you have vista or later, right click "my computer" and click on "manage".
when the window loads up you should see an options bar on the left hand side and an option called "disk management" click this option and wait for the window to load
now you should see what partitions you have (the 35GB and remainder)
right click the 35GB partition and click "extend volume", this should tell you what unallocated space you have and on what HD the unallocated space is on.
for example there should be a column on the left hand side saying "disk 1 XXXXGB free" (or summin like that) and a column on the left, with options in the middle.
i cannot remember the exact options in the middle but basically you want all the unallocated space to go into the column on the right, this right hand column is the space the original volume is expanding into (if this isn't clear, sorry but im trying to describe it as best i can)
anyway once you use the options in the middle to get the free space into the right hand column click next and follow the on screen instructions if your not already
(PLEASE NOTE) it WILL take a while to expand the volume and its important you just let the computer do its thing, it may appear asif it has frozen, but it has not (trust me it takes a while i've done it before) it may help if you close all background programs and windows (bottom right .... right click ... quit/exit/stop, whatever the case maybe, if its something like anti-virus software don't worry because it might be more hassle starting it again afterwards)
hope this helps