An employer can at any time apply for your LMO for a new position, even if you haven't been in Canada for a year. If your LMO is denied, you stay in your low skilled job with your low skilled permit. If it accepted, you can apply for a new work permit for your skilled position. If it is granted, if it is with a different employer, you can no longer work for the old employer.
With a skilled work permit, you would have the option of applying for an open work permit for your spouse based on your work permit and after 2 years of working on a skilled permit, you can apply for your PR under Canadian experience class. You would also have more options to be sponsored for PR by your employer under PNP. There are some low skilled options under PNP in BC and AB but only for certain occupations and under certain conditions.
The skilled worker program on the other hand has nothing to do with skilled or low skilled work permits. That is a program to apply for your PR. You need to have 67 points and at least one year of continuous skilled work experience. You also need to meet the requirements for one of 3 categories, 1 is having an occupation on immigrations most wanted list, 2 is having an approved job offer (skilled) in Canada and 3 is having been working or studying in Canada for 12 or more months, not specified that this 12 months has to be skilled.
You can find links to all the immigration programs, including skilled worker at http://www.cic.gc.ca/english/immigrate/index.asp